Mistakes in the Harry Potter books

"As obsessive fans will tell you, I do slip up! Several classrooms move floors mysteriously between books and these are the least serious continuity errors! Most of the fansites will point you in the direction of my mistakes. But the essentials remain consistent from book to book because the story has been plotted for a long time and it is clear in my mind."

- J. K. Rowling on the errors within the franchise.

Below is a list of mistakes that occur in the Harry Potter book series.

Harry Potter and the Philosopher's Stone

 * Much of the first chapter talks about wizards celebrating the fall of Voldemort all day long, yet Harry's family was attacked at night; unless it took Hagrid 24 hours to get Harry from his parents' ruined house to Little Whinging, this seemingly does not make sense. A possible explanation, however, is that it does not say when Hagrid pulled him from the house. It could have been a full day until they could respond, or he could have kept Harry with him until night, when he could easily fly under cover of darkness to Little Whinging. He could have also gone to get the baby Harry checked over to see if he had been harmed. The day, however, is November 1st, the day after Voldemort's downfall, so the celebrations are happening after his downfall the evening prior.
 * The beginning of the story takes place on a "dull grey Tuesday." In 1981, however, Oct 31 was on a Saturday, placing the celebrations on Nov 3. This makes what the TV weatherman wrong as he admonished people that Bonfire Night was the next week. In fact, it would have been in two days.
 * The boa constrictor at the Zoo winked at Harry during their conversation. And while snakes do have eyelids, it is impossible for snakes to blink like the boa constrictor did to Harry, their eyes being protected by transparent scales.
 * Harry's 11th birthday, 31 July, was a Tuesday. But in 1991 in the real world, that date was a Wednesday.
 * When Harry and Hagrid are leaving the little shack out in the middle of the sea, they used the rowboat that the Dursleys' had borrowed in order to leave the rock. This leaves the Dursleys with no way to get back to shore, yet there is no mention of retrieving them, and it is implied Harry goes straight back to Privet Drive after his shopping at Diagon Alley.
 * On Harry's Hogwarts list of school supplies, "1 Wand" is listed twice, as both the first and last item on the list. (Rectified in later editions)
 * It states in the Hogwarts letter that you can bring an owl, toad, or cat. Ron brings his rat Scabbers. It is possible, however, that the rules are leniently enforced, or despite those specific animals being listed, there is no specific prohibition against other types of animals.
 * The air in the tunnels to the Gringotts vaults is described as getting colder as they go deeper. This only happens very near the surface, and only when the weather has been relatively warm. Once you get below the level where the temperature depends heavily on the seasons at the surface, the geothermal gradient takes over, and it gets hotter as you go deeper. In the world's deepest mines, the miners can only work for a short time before being brought back up, because of the risk of heat stroke.
 * Much importance is placed on the theme of wandlore and wand ownership throughout the series, so it seems odd in retrospect that, during Harry's first meeting with Draco Malfoy in Madam Malkin's, he should mention that his mother is away looking at wands. Indeed, it is just as odd to hear that Ron has been equipped with Charlie's old wand. It is mentioned, however, in Deathly Hallows and on Pottermore that there are old superstitions about wands and what kind of people are chosen by certain wands and so it's possible that Narcissa Malfoy had certain beliefs along those lines. As for Ron, his parents probably could not afford to buy him a new wand at the time. This was probably meant to show that his family was not very well off in terms of wealth. Even though it is better to have your own wand, a person can still do magic with another person's wand.
 * When Harry is talking to Hagrid about his first meeting with Draco Malfoy, Hagrid says that "there's not a single witch or wizard who went bad that wasn't in Slytherin." At the point when this conversation takes place, Hagrid (along with the rest of the wizarding world) would have been under the impression that Sirius Black, a Gryffindor, was responsible for betraying Harry's parents. This, however, is potentially simply an instance of the literary device of hyperbole ("the use of a statment to evoke strong feelings or create a strong impression, but not meant to be taken literally"), rather than ever being intended as an accurate historical statement, even if one ignores the fact that there are known to be dark wizards from other schools, such as Grindelwald.
 * Hermione Granger says that she has been practising spells at home, but this is against the Decree for the Reasonable Restriction of Underage Sorcery, which normally results in a warning letter. Hermione, however, was Muggle-born, and had not yet started school, so it is possible that Muggle-born children are not informed of these rules prior to starting school. Alternatively, it is also possible that she practiced the wrist movements one does when executing spells, or the correct pronunciation of the spells, rather than the actual execution of the spells.
 * While being Sorted into houses, Harry looks up at the Sorting Hat's stool, and there are only three people left to be sorted. Professor McGonagall then calls out the names of four more students. (Rectified in later editions)
 * When Harry first met Nicholas de Mimsy-Porpington, the ghost says he had not eaten in nearly 400 years. Yet he had, at the time, already been dead for 99 years longer than that. (Rectified in later editions.)
 * Harry buys the book One Thousand Magical Herbs and Fungi, but later, he looks up "dittany" in One Hundred Magical Herbs and Fungi. (Rectified in later editions.)
 * Fred Weasley says that Gryffindor has not won the Quidditch Cup since Charlie left. According to J.K. Rowling, Charlie is three years older than Percy who is in his fifth year, meaning that Charlie would have left the year before. So basically Fred is saying that Gryffindor has not won since last year. Professor McGonagall also said that Gryffindor was flattened in the last game between Gryffindor and Slytherin. While this is not an outright mistake, it is still somewhat confusing. Another confusing part is that readers confuse the Quidditch Cup with the House Cup. At this time Slytherin was on a six-year winning streak with the House Cup, not the Quidditch Cup.
 * During the Hallowe'en feast, when the troll is let in, Professor Dumbledore sends the students to their dormitories. However, the troll is said to be in the dungeons, and that is also where the Slytherin dormitories are, meaning Dumbledore has put them directly in harm's way by sending them there. He did, however, send the sixth and seventh years with them and given that the Trio were able to handle a single troll on their own, one would not be able to overcome that many wizards.
 * During the match against the giant chess set, Ron says, "Well Harry, you take the place of that bishop, and Hermione, you go next to him instead of that castle." But the castle is next to the knight, not the bishop. It is, however, possible he meant "next to him" to mean "on the same side of the king and queen."
 * At the beginning of the chess match, Ron is the knight in the giant chess set. However, it later says that he had to "move ahead one" so the Queen could take him, opening the path for Harry to checkmate the king. If he was a knight, he could only move 1) ahead one, sideways two, or 2) ahead two, sideways one, like an "L." It is possible this meant "one" as in a single move, but it is still an odd construction regardless.
 * Flint is referred to as a burly 6th year, but he is in book 3, meaning either his age was forgotten by J. K. Rowling, or he dropped a year. It was later confirmed by Rowling that Flint failed his N.E.W.T.s and had to repeat his seventh year.
 * On Page 173 of the UK paperback, in "Norbert the Norwegian Ridgeback", it says "Wednesday night found Harry and Hermione sitting alone in the common room, long after everyone else had gone to bed. The clock had just chimed midnight...." However in Chapter 8, "The Potions Master", it is mentioned that Astonomy classes take place every Wednesday at midnight. Therefore, they are presumably skipping class, and the other students should not be asleep.

Harry Potter and the Chamber of Secrets

 * The Hogwarts' equipment list mentions the Lockhart book "Wanderings With Werewolves," but later, Lockhart refers to the book as "Weekend With a Werewolf". (Fixed in later editions.)
 * The cover illustration of Harry, Ron and Hedwig in the flying Ford Anglia incorrectly depicts Hedwig as a Barn Owl rather than a Snowy Owl.
 * When Harry and Ron arrive at Hogwarts in their father's flying Ford Anglia (a scene which takes place on 1 September 1992), they are told that they had been seen by Muggles in various situations, including flying past the "Post Office Tower". Quite apart from the fact that a change of ownership means that the building in question has been called the "BT Tower" since 1984, said building is about a mile south-west of King's Cross, so to be passing it, Harry and Ron had to be going in entirely the wrong direction to be following the Hogwarts Express, or even the tracks generally.
 * After Harry, Ron, Fred, and George arrive at the Burrow after getting Harry, Mrs. Weasley shouts at Fred first. "You will not," then she says "And you two,"" glaring at Ron and Fred. It should say George, as she has already yelled at Fred. (Fixed in later editions.)
 * Dumbledore tells Harry at the end that Lord Voldemort is the last remaining ancestor of Salazar Slytherin. But ancestors are in the past - he means Voldemort is the last descendant of Salazar Slytherin. (Corrected in later printings.)
 * Hermione says Moaning Myrtle haunts the bathroom on the first floor. However, when Harry sees the writing on the wall outside her bathroom, he is on the second floor. This is explained by the fact that in the UK, the ground floor is the floor on which the entrances are, and the floor above it is the first floor, and this was one of the few edits made for the North American release, despite the criticism on edits for Philosopher's Stone.
 * When Harry is viewing the memory from Tom Riddle's diary, Tom Riddle says to Hagrid at one point, "The dead girl's parents will be here tomorrow." It is stated elsewhere in the book that Myrtle is Muggle-born. Muggles cannot enter Hogwarts. It is possible, however, that an exception was made for them; that the Muggle-Repelling Charm could be lifted a day or two, for this reason. Considering that the Grangers were able to enter Diagon Alley without any problems when normal Muggles could not see The Leaky Cauldron, this theory is somewhat strengthened.
 * 14th February 1993 is Sunday in the real world, yet in the book the students had their classes on that day as Harry got his 'musical message' when he walking upstairs for Charms.
 * When Harry speaks Parseltongue to the snake during his duel with Draco, everyone hears him hissing. Therefore, when Harry hears the basilisk speaking in the walls, Ron and Hermione should hear hissing, yet they claim to hear nothing. They might, however, hear pipes hissing but subconsciously ignore it, dismissing it as creaking wood, an air current going through the pipes, or other animals such as mice. Alternatively, it could be that the snake is simply making a very quiet hissing. The basilisk's voice is implied to be a whisper and Harry, being the only one to hear English words, would be the only one to notice anything.
 * The first day of term is always the 1st September, the next day is always a Monday. This is impossible, due to the fact that the year does not have 364 (divisible by 7) days.
 * On page 283 of some copies of the U.S. paperback edition, the word professor is spelled as professorr.
 * Percy's name is spelled Perry (Fixed in later editions)

Harry Potter and the Prisoner of Azkaban

 * Fred and George Weasley had the Marauder's Map before Harry did, so if Harry can see Peter Pettigrew in the map, then Fred and George seemingly ought to have noticed that Pettigrew was sleeping with Ron every night. They did, however, tell Harry that they found the map in their first year, and no longer need it as they "know it by heart", so it is possible that they have not used it since Ron (and Scabbers) arrived at Hogwarts, or that they believed that the map made a mistake, that conclusion having been drawn by Harry. It is also entirely possible that the twins simply had no interest in using the map to look at their brother sleeping.
 * The first chapter says that A History of Magic was written by Adalbert Waffling, rather than Bathilda Bagshot. (Rectified in later editions.)
 * Given that Remus Lupin had a transformation sometime after Halloween but before the following weekend (the day of the Gryffindor-Hufflepuff match), the full moon would have had to be sometime in the first week of November, probably the 4th or 5th of November as he was absent from class on the Friday before the match. As the full moon occurs every 29-30 days, by that time frame the December and January full moons would also have occurred sometime around the 3rd-5th of those months. Therefore a full moon during the Christmas Eve to Boxing day period is not possible. Yet Dumbledore explains to Trelawney that Lupin's absence from the Christmas dinner is that he is not well again - implying either a transformation or post-transformation exhaustion, especially as Snape is mentioned as having brewed his potion for him. It is not specified, however, in the books how long a werewolf might suffer ill-effects from transformation, and how much variation there is between months. Therefore, he may simply be suffering pre-transformation effects and, as the Wolfsbane potion must be taken in the week preceding the full moon, then the next full moon may be as late as New Year's Eve. Notably, Snape says in the Shrieking Shack that Lupin had not taken his potion tonight, but it is explained he must drink the Wolfsbane Potion the week before transforming, not on the night itself, so missing the potion shouldn't have affected him within the space of a few hours.
 * Before Harry and Hermione go back in time, it mentions that Buckbeak is tied to a tree. But when they go back in time, Buckbeak is tied to a fence.
 * When Harry is buying his books at Flourish and Blotts, it mentions that he is being served by the manager. But when Harry was staring at the book 'Death Omens', it says that he is being served by the assistant of the store, though it is possible that the manager was simply the assistant to the shop owner.
 * In June, Fred and George Weasley find out they have scraped "a few O.W.L.s apiece". However, in subsequent books, it is firmly established that O.W.L. results are sent home by owl and are not received until August. Yet it is possible that they snuck into an office and retrieve the information of their results or were assuming that they got low marks.
 * Mr. Weasley says that Ron and Harry have ended up in the Forbidden Forest twice. But only Harry has been in the forest twice. Ron went once to see Aragog with Harry in the 1992-1993 school year, but the other time Harry went was for detention in the 1991-1992 school year, and Ron was not there (he was in the film, but not in the book).
 * Chapter sixteen (Professor Trelawney's Prediction) takes place in June 1994. In the beginning of that chapter, Harry Potter reads a note from Hagrid and says, "Buckbeak's appeal — it's set for the sixth." The night after the Hippogriff's appeal, Remus Lupin is forced into a werewolf form by the full moon, which means that this happened on the night of June 6th, 1994. The web page HP-Lexicon.org also backs this up. However, a brief look at lunar phase calendar sites such as 1994 and lunar phases in 1994 definitely shows June 9, 1994, as a new-moon night, which means that a full moon could not possibly rise three days earlier.
 * On the American version of the cover, the front art is the night that Harry and Hermione save Sirius and Buckbeak. However on the back side of the cover (Lupin appears as a werewolf), the moon is crescent when it should be a full moon.
 * The cover of the Scholastic edition depicts Harry and Hermione riding Buckbeak. Harry's legs are shown to be in front of Buckbeak's wings. However, when Harry was in Care of Magical Creatures and rode Buckbeak for the first time, Hagrid had told him to sit behind the wing joint (as he did in the movie). Although, it could be because Hermione is sitting behind him.
 * Sirius Black says that Voldemort has been in hiding for fifteen years. He has actually been in hiding for twelve years (almost thirteen at the time that he says it), about the same amount of time since Black was imprisoned. Voldemort went into hiding right after he was ripped from his body after failing to kill Harry. Of course, Black could just be rounding off to an approximated number (fifteen years), but this seems unlikely since he keeps talking about being in Azkaban for twelve years, being that the two time frames are almost exactly the same. Sirius also says to Pettigrew "you haven't been hiding from me for twelve years, you've been hiding from Voldemort's old supporters." Voldemort could, however, have been hiding to escape capture and operating secretly before killing Lily and James Potter.
 * In the last chapter on page 284, it says Dumblefore instead of Dumbledore.
 * On the back cover it says Harry blew up his horrible Aunt Petunia instead of Aunt Marge
 * Ernie Macmillan's last name is misspelled McMillan.
 * On page 379-380 of the American paperback edition, when exiting the tunnel that lead out of the Whomping Willow, it was Crookshanks, Lupin, Pettigrew, Ron, Snape, Sirius, Harry, and Hermione. Later on when Hermione used the Time-Turner (page 408), and she and Harry were watching the Whomping Willow to see themselves coming out the order changed to Lupin, Ron, Pettigrew, Hermione, the unconscious Snape, Harry, and Sirius. They could have simply missed Crookshanks exiting, though there is no explanation for the change in order of the visible humans.
 * Sybill Trelawney told Lavender Brown that the worst thing for her would come true on Friday, 16 October. However, 16 October, 1993 was a Saturday.
 * When Harry gets back into the Gryffindor common room shortly before the Gryffindor-Ravenclaw match with his Firebolt given back to him after being tested for jinxes, the common room admires the broom. An unidentified Gryffindor tells Harry, "Ravenclaw'll have no chance, they're all on Cleansweep Sevens!" However, later in the book, Oliver Wood tells Harry that Cho Chang, the Ravenclaw Seeker, rides a Comet Two Sixty. It is possible, however, that the unidentified Gryffindor who told Harry this probably doesn't know much about the Ravenclaw Quidditch team or meant that most, not all, of the Ravenclaws ride Cleansweep Sevens.
 * On page 101 of the American hardcover edition, Sybill Trelawney's name is misspelled as 'Sibyll'.
 * In Chapter 15 (The Quidditch Final) when Katie Bell is taking her second penalty shot at the Slytherin vs. Gryffindor, it says she put it past the Slytherin Seeker. The Seeker in Quidditch is the one who chases the Snitch, which, in the case of Slytherin, would be Draco Malfoy.

Harry Potter and the Goblet of Fire

 * In the book's opening chapter, there are repeated references to a planned murder, with lines such as "...one more death and our path to Harry Potter is clear" and "One more murder… my faithful servant at Hogwarts…" Yet, there is no indication that anyone else is murdered that was part of this plan. Bertha Jorkins was already dead, Frank Bryce was only a victim of circumstance, and Barty Crouch was originally kept alive and only killed because he had escaped and become a liability. Voldemort's original plan may have been to kill Crouch Sr., and he was subsequently convinced otherwise by Wormtail or Crouch Jr., though if so, nothing was ever explained.
 * In Back to the Burrow Mr Weasley puts a pinch of Floo Powder into the fire for their group to return to the Burrow, but in book 2 everyone has to use Floo Powder individually to travel.
 * Towards the end of the book when Voldemort puts the Imperius Curse on Harry the book says "For the third time in his life," when towards the middle of the book it states Harry had the Imperius Curse put on him four times by Moody (Crouch).
 * However Rowling may have been referring to the number of occasions and situations on which it was used, rather than the exact number of times the curse was said.
 * Harry's fourteenth birthday is on July 31, 1994 but in his letter to Sirius at the beginning of the book he mentions that his cousin Dudley got really angry and chucked his PlayStation out of the window. The PlayStation was not released in Europe until September 29, 1995. It could not have been imported either, because the PlayStation was not released in Japan until December 3, 1994. However, it is possible that the Dursley's had signed up to be product tester, which would mean that they would receive the product (in this case, a PlayStation, and a couple games) months before the product was released. It is possible that Harry, due to his lack of interest in the materialism of the Dursleys, had confused the PlayStation with a similar console.
 * In what is now known as the "Wand Order Mistake," when Harry and Lord Voldemort's wands engage in Priori Incantatem while in the graveyard James Potter exits the wand before Lily Potter. It has always been said that James died first as he was trying to give Lily and Harry time to flee, and since victims of Lord Voldemort were exiting the wand in reverse order of being killed it was thought to have been a clue from J.K. Rowling. Rowling later said that "late night writer's fatigue" was the reason and the error has been fixed in later editions.
 * During the meeting between Fudge, Dumbledore and Moody, Fudge is mistakenly referred to as both "Crouch" and also as his first name, "Cornelius."
 * In the European and Canadian versions of the book, Snape shouts "Ten points from Hufflepuff, Fawcett! And ten points from Ravenclaw too, Stebbins!". Really, Fawcett is in Ravenclaw, and Stebbins is in Hufflepuff. It may, of course be, that Snape, angry as he was, mixed up the two student's affiliation to the houses. The American version corrects this error, but in a deleted scene from the film, included in the uncut DVD, Fawcett is again the Hufflepuff, and Stebbins the Ravenclaw.
 * In Quidditch Through the Ages, it says that the first ever World Cup was in 1473, with a match being held every 4 years. Yet the World Cup in 1994 is number 422. There cannot be 422 world cups in 521 years with a four-year gap in between.
 * Before the third task starts, Molly Weasley reminisces about the gamekeeper before Hagrid, named Ogg. But in other books, it is implied that Hagrid has held that post since his expulsion from school in 1943. Since Hagrid's years as gamekeeper appear to overlap Molly's years at school, it seems unlikely that she knew a previous one. Either that or Hagrid originally started off as Ogg's assistant.
 * Hagrid was more than likely to start off as his assistant as he was still very young when he was expelled from Hogwarts, as Hagrid himself states in the first book.
 * When Fred and George bet on the Quidditch match with Bagman, it says Fred put the paper with their wages in his robes, but Fred was wearing Muggle clothing.
 * Barty Crouch Sr. mentions that his son got twelve O.W.L.s. Once again this is inconsistent with the time-table clashes from Prisoner of Azkaban. However, given Crouch Sr.'s damaged state of mind, he could have just been rambling insanely. Either that or with his position in the Ministry, it is possible that he obtained a time-turner for his son. Another possibility is that it is not necessary to take a class in order to sit an O.W.L. This is logical since Remus Lupin mentions in Deathly Hallows that until Voldemort took over the Ministry, parents were allowed to educate their children at home, though virtually all British magical children attended Hogwarts. These students would presumably need the credentials given by an O.W.L. or an N.E.W.T. in order to obtain employment in many occupations. It is thus possible that a highly motivated student may be able to do "independent study" to achieve an O.W.L., or that a student was already so familiar with the Muggle world, for example, that they could easily pass an O.W.L. in Muggle Studies without attending classes.
 * In some printings, the spell to revive Krum and Crouch from unconsciousness is enervate. The correct spelling is ennervate, as enervate would have the opposite effect.
 * The notice that says classes will end a half hour early for the arrival of the Durmstrang and Beauxbatons students states that October 30, 1994 is a Friday. However, it was really a Sunday.
 * In the American paperback on page 148, Harry asks Ron if he can dump his things upstairs in his room. It then states: "'What's up Harry?' said Ron, the moment they had closed the door of the attic room behind them." In Harry Potter and the Chamber of Secrets American paperback page 41 Ron says "...I'm right underneath the ghoul in the attic" referring to his room. Therefore the sentence in Goblet of Fire where he closes the attic door (to his room) does not make sense because that is where the ghoul resides.
 * However, taking into account that Bill and Charlie were in the Burrow as well, Ron could have been moved to the attic for the time being, giving Bill and Charlie his room.
 * That is unlikely, as the ghoul already resides in the attic. Therefore Ron moving to the attic would mean he sleeps in the same place where the ghoul lives.
 * In the American paperback page 498 (Ch 26 - The Second Task) it says that Ron was tied between Hermione and Cho Chang. After Harry cuts Ron loose, it says on page 500 that Cho's head was on Hermione's shoulder, but would not they be too far apart for her head to be resting on Hermione's shoulder?
 * Maybe they had, being under water, drifted over to each other now that Ron was out of the way.
 * Near the beginning of Chapter 14, Neville is assigned the task of disemboweling horned toads as punishment from Professor Snape. When Hermione teaches him the Scouring Charm to remove the filth from under his fingernails, they're referred to as "frog guts". However, the horned toad is actually a species of lizard, despite the name.
 * As it was from Harry's point of view, he might not have known that fact and simply assumed the horned toad was a species of frog.
 * On page 594 in the First Edition of the Canadian paperback when Dumbledore is questioning Barty Crouch, it says: "'How did your father subdue you?'" said Dumbledore. "'The imperius curse,'" said Moody." Crouch is mistakenly referred to as Moody in this sentence because it was after Barty Couch had already returned to his original physical state (no longer an impersonation of Moody). Crouch had already been referred to by his real name earlier on that page, and the real Moody was lying stunned at the bottom of the trunk in his office.

Harry Potter and the Order of the Phoenix

 * In the American paperback page 161, when talking about the old Defence Against the Dark Arts teachers, Harry says, "One sacked, one dead, one's memory removed, and one locked in a trunk for nine months." referring to Lupin, Quirrell, Lockhart, and Moody respectively. However, according to PoA American paperback page 423, Lupin did not get sacked, he resigned. Although, Harry could have interpreted Lupin's resignation as forced by Snape's revelation of his lycanthropy, and therefore considering it the same as a sacking.
 * Moody was locked in a trunk for ten months (from the beginning of September to the end of June.)
 * Also, Fred does not mention either of his first two DADA teachers, even though in Half-Blood Prince Dumbledore says that the job is jinxed and that nobody has lasted more than a year. However, since the context of this discussion was how unappealing the job is, it is possible that no physical harm came to Fred's first two DADA teachers; they may have just taught for one year and then resigned.
 * In Chapter 3, when the Advance Guard arrives at 4 Privet Drive to take Harry to 12 Grimmauld Place, Harry is already in trouble for casting a Patronus Charm in the presence of a Muggle. Yet, Tonks casts several spells (Lumos, a packing spell, Scourgify, Locomotor Trunk) and Moody casts a Disillusionment Charm on Harry while they are still at 4 Privet Drive. Lupin had clearly stated that they were not using the Floo Network because they were being watched (by the Ministry), so of course the Ministry was not aware of any Wizards that are allowed to do magic were inside Harry's house. If the Ministry can detect magic, and Harry is the only known wizard in Little Whinging, then he should have either had another owl sent from the Improper Use of Magic Office or the uses of those spells should have been brought up at some point during his trial.
 * There is a slight possibility that the Minister or a Ministry employee had spoken to Dumbledore about this previous to Harry's trial.
 * Also, given that the Dursleys had left before the Advance Guard arrived, the house did not have any Muggles currently inside, so, unlike when Harry performed the Patronus Charm only a few feet away from Duddly, there were not any Muggles present.
 * Furthermore, it is mentioned in the Deathly Hallows that a wizard's Trace is removed once they come of age, so the Ministry would not be able to know about spells cast by registered wizards, however when Dobby cast magic in Chamber of Secrets he did not need a wand and so presumably the ministry did not keep records of House-Elves. Also Lupin implies that the Floo Network is being watched, not necessarily every spell cast.
 * Sirius Black told Harry Potter that Bellatrix ran in the same crowd as Severus Snape while at Hogwarts, but her date of birth makes this impossible. Bellatrix would have attended Hogwarts from 1962 to 1969, or possibly 1963 to 1970, depending on which month in 1951 she was born in, whereas Snape began his schooling in 1971. This may simply be an error, as J. K. Rowling has admitted that math is not her strong suit. Another possible explanation could be that both Bellatrix and Snape went around with the same type of people, some of whom may have overlapped depending on age
 * Ginny Weasley's birthday is on the 11th of August, the day before Harry's trial. The day before the trial is mentioned, but Ginny's birthday is not.
 * During Harry's hearing, Cornelius said that he blew up his aunt three years ago. However, the incident when Harry inflated Marjorie Dursley occurred almost exactly two years previously.
 * In chapter 9, Ron's prefect badge is described as scarlet and gold. Page 162 of the American paperback states: "A large P was superimposed on the Gryffindor lion. He had seen a badge just like this on Percy's chest on his very first day at Hogwarts." However, Percy's badge in Philosopher's Stone is described as silver with a P on it.
 * In chapter 9, Mrs. Weasley says that everyone in the family has been a prefect, but Charlie was a Quidditch Captain.
 * During the meeting in the Hog's Head, Dennis Creevey shows up for the meeting. However, in Harry's fifth year, Dennis would only be a second year, and therefore would not be able to visit Hogsmeade. He could, however, have snuck out of the school with his brother.
 * In chapter 9, when Harry lets Hermione borrow Hedwig, Harry remains bent double until he hears Hermione close the door. However, when he hears Hermione and Hedwig had gone, he hurries across the room and closes the door, but the door had already been closed.
 * But it is also possible that the door have not been closed properly, and thus reopened, so Harry checked the door to be properly closed in order to be alone.
 * After Harry has seen his father bully Snape in a memory, he remembers Professor McGonagall saying that James and Sirius were troublemakers at school, but no more so than the Weasley twins. This is incorrect. She said in the Prisoner of Azkaban that she had no memory of anyone else being so troublesome, and Hagrid said Fred and George could have given them a run for their money.
 * In chapter 30 of the American hardcover, Harry and Hermione find seats in the topmost row at the Quidditch match. But when Hagrid comes to tell them about Grawp, he squeezes his way through the row behind them. If Harry and Hermione are in the topmost row, there cannot be a row behind them. (Corrected in later editions)
 * In Chapter 31 "O.W.L.s", it is stated that the practical Astronomy O.W.L. began at 11:00 pm, and Harry observed Venus one hour later (12:00 am). However, Venus can only be observed shortly before sunrise, or shortly after sunset, it can never be seen at midnight. Harry was also filling in his star chart with the stars in the constellation of Orion, however Orion would have set before 11:00pm on that date.
 * Also, Hogwarts is somewhere in the Highlands of Scotland (according to the movie of Prisoner of Azkaban, it's near Dufftown in Moray); at that latitude, in the two months either side of June 21, the sky never gets completely dark. There is at least one website showing that sunset on the day of the examination would be about 11pm — the time the examination is supposed to start. It would be unlikely to be dark enough to observe any but the brightest stars.
 * When Hagrid returns and begins teaching his class again, he comments that he has been bringing Thestrals for his fifth years' O.W.L.s for years. But he only became a teacher two years ago, in Prisoner of Azkaban.
 * But he has been a gamekeeper for many years, and it is very much possible that teachers have asked him to bring them over the years.
 * In chapter 37, after Sirius' death, Harry reminisces about when Sirius watched him play Quidditch in Harry's third year. Harry wonders if Sirius had come to see if he was as good a player as James had been, and regrets never having asked him. However, in Prisoner of Azkaban Sirius specifically tells Harry that he did watch him for that exact reason, and that he was as good as his father.
 * It is possible that Harry could have forgotten this. This is quite possible, as it had already been nearly two or so years.
 * During the Ordinary Wizarding Level examinations, Hannah Abbott was doing her transfiguration practical at the same time as Harry Potter. This is odd as the examinations are done by surname, meaning that Hannah should have finished a while ago, unless she was a rather incompetent student, or unless she had a fit of anxiety in the middle of the examination and had to be calmed, which could take time, and then resume the exam when Harry started his.
 * In an error unique to the U.S. audiobook editions of Harry Potter and the Order of the Phoenix, when Harry first arrives at 12 Grimmauld Place following his vision of the attack on Arthur Weasley, the line "Back again, the blood-traitor brats! Is it true their father's dying?" is rendered in the loud, screechy voice of Sirius Black's mother. Based on context clues, however, particularly the fact that this line is immediately followed by Sirius shouting "Out!" and Kreacher shuffling out of the room, it seems clear that it was actually Kreacher that uttered the insults, not Mrs. Black.
 * Not completely sure if it is an observation more than a mistake, but Seamus Finnegan doesn't join Harry's DA Lessons at first because he thinks he's a liar, although Hermione says Lavender Brown thinks Harry is a liar too, yet she takes Harry's stories for granted when he is asked what spells he can cast in the Hog's Head.
 * in Order of the Phoenix Hermione begins to use the word "Voldemort", albeit rather hesitantly, and scolds Ron for not doing the same. However, in "Hagtid's Tale" on Page 382 of the UK paperback, she reverts back to saying You-Know-Who. This may be because she is talking to Hagrid, but nonetheless it is still rather hypocritical.

Harry Potter and the Half-Blood Prince

 * On page 225, it states that Jimmy Peakes and Ritchie Coote join Katie, Demelza and Ginny in the stands for the selection of their last team member, the Keeper. Yet, on the next page, when McLaggen missed the 5th goal, he told Harry concerning Ron's success, "His sister didn't really try.... She gave him an easy save," implying that Ginny and the other team members had been out on the pitch testing the potential Keepers instead of sitting in the stands.
 * It is possible that Harry gave the Keepers other tests before trying them with the Chasers. Or, he may not have called the Chasers up at the time of Peakes and Coote sitting down and so they were still sitting in the stands where they had gone during the Beater's try-outs.
 * On page 101 of the British version, Ron mentions that Hermione got ten Outstandings and one Exceeds Expectations for Defence Against the Dark Arts giving her a total of eleven O.W.L.s. However, as she dropped both Divination and Muggle Studies in her third year, she could not possibly have got eleven O.W.L.s as she was only doing ten subjects - Transfiguration, Charms, Herbology, Potions, Defence Against the Dark Arts, History of Magic, Astronomy, Care of Magical Creatures, Arithmancy and Ancient Runes.
 * This was corrected in the Scholastic editions, where Ron instead says nine Outstandings and one Exceeds Expectations.
 * On Harry's sixteenth birthday, Remus Lupin tells Harry that Garrick Ollivander has gone missing. But in Harry Potter and the Deathly Hallows, it said that Ollivander had been in the Malfoys' cellar "a year". However, if he had been captured at the beginning of the sixth book, he would have been held in the cellar for about two years. However, this could mean that Ollivander was held in a separate place for a year before being moved to Malfoy Manor.
 * Considering Lord Voldemort had only recently started using Malfoy Manor as his base by the time of Deathly Hallows Chapter 1, and more than one raid was done on the manor itself by Arthur Weasley and his office and he was not found, the latter option seems the likely case.
 * Harry's sixteenth birthday happens on July 31st, 1996. Looking at any full moon calendar, in that year full moon was on July 30th. Remus Lupin was recovering from the after effects of his werewolf transformation and it is therefore difficult for him to go to birthday parties. It is said, though, that he was looking "gaunt and grim", so he might have transformed the night before.
 * There are other times when the full moon does not occur in the books the day it did in real life.
 * At Christmas, however, it is stated that Remus Lupin comes over to the Burrow and even uses Bill's bedroom. December 24, 1996 is the exact date of a full moon and, since Lupin was already living with the werewolves, there was little chance he could get the seven days doses of Wolfsbane potion required to make him harmless. Therefore, on that night he would have been a dangerous transformed werewolf.
 * In the chapter titled "The Secret Riddle", "... Dumbledore entered the room ... It was a small bare room with nothing in it except an old wardrobe and an iron bedstead." A couple paragraphs later, "Dumbledore drew up the hard wooden chair beside Riddle, so that the pair of them looked rather like a hospital patient and visitor."
 * With Dumbledore especially, the term "draw up a chair" is used literally several times when Dumbledore magically conjures a chair by drawing it. This may have been a covert way of implying this, especially considering Riddle may have missed this action by Dumbledore.
 * On page 342 of the American version, there is a punctuation error when Molly Weasley says "Have a little purkey, or some tooding...I mean-" to Rufus Scrimgeour. There are no quotation marks in front of the have in the statement. This is corrected in the newer editions, however.
 * In Snape Victorious Snape deducts 50 points from Gryffindor so that they're in the negative, but at the end of book 5 Snape can't deduct points as Gryffindor doesn't have any.
 * At the start of term feast, Dumbledore tells Quidditch hopefuls to put their names down for selection. For the Gryfindor House at least, there had never been trials before. Katie Bell also warns Harry against just "picking the old faces" but this had automatically been the case for the 5 years preceeding Harry's 6th year.
 * However, it is likely Wood was happy with the team for those five years, and there was no reason to hold a trial with no spots becoming vacant up until he left.

Harry Potter and the Deathly Hallows

 * When Harry, Ron and Hermione are camping and they get caught by the Snatchers, Hermione pretends she is Penelope Clearwater, but Penelope was Petrified in book 2, therefore she is Muggle-born so she would also be on the Muggle-Born Registration Commission list.
 * This may not be the case. Harry and Ron speculate that after Hermione discovers the truth about the chamber and the Basilisk "she told the first person she met to look around corners with a mirror." Seeing Hermione came across Penelope and got her to look around the corner, there is a possibility that she [Penelope] was not muggle born.
 * Near the end of chapter thirty, it says that the only people left in the Room of Requirement are Harry, Ginny, Mrs. Weasley, Lupin, Fred, George, Bill and Fleur. But on the next page Percy (who had recently entered the room) apologises to Mr. Weasley, but Mr. Weasley had left the room along with all the other people.
 * When Harry is viewing Snape's memories, he witnesses a scene on Platform 9&frac34; between his mother and Aunt Petunia, in which Petunia tugs her hand out of Lily's grasp. Her hand is then back in Lily's and she tugs it out again.
 * Along a similar vein, if Petunia had been on Platform 9&frac34; before, she should have known where it was and been able to tell Vernon. It is possible however that she either had forgotten or neglected telling Harry out of spite.
 * When Harry stuns Umbridge and Yaxley in the courtroom, he "whirls around" to see dementors approaching Mrs. Cattermole. But Harry was already facing her, having been seated behind Umbridge, Yaxley, and Hermione.
 * It might have been that the Dementors were approaching Mrs. Cattermole at a distance, and they were not directly in Harry's line of vision.
 * When Harry talks to Griphook about breaking into Gringotts, Griphook has the Sword of Gryffindor in his hands. When Harry stands up to leave a few moments later, the sword is now beside Griphook's bed.
 * At the beginning of chapter two, it says that Harry can not use magic due to not coming of age for 4 days. In chapter six, days have passed since the Battle over Little Whinging, but Harry states the Trace will break in 4 days.
 * However with everything that was going on Harry's mind may have become confused or he could have just said the wrong thing.
 * When Harry, Ron, and Hermione leave the Great Hall after the Battle of Hogwarts ends, Harry is under his Invisibility Cloak, and remains under it when they reach the Headmaster's office. When Harry raises his arms to silence the headmaster and headmistress portraits, he is suddenly visible to everyone, but there is never any mention of him taking the Cloak off.
 * When Harry, Ron and Hermione are at the front door of Xenophilius Lovegood's house, Hermione says to Harry, "You better take off the Invisibility Cloak, Harry, it's you Mr. Lovegood wants to help." and he handed her his Cloak to place in the beaded bag. But later after the Death Eaters arrive Hermione says "Harry give me the Invisibility Cloak, Ron, you're going to put it on."
 * Also, in the Room of Requirement when Harry, Ron, and Hermione are talking with Malfoy, Crabbe, and Goyle, it says that Crabbe's voice was soft. But in the second book, when Ron turns into Crabbe after drinking Polyjuice Potion, Ron's voice also changes along with the appearance. So his voice became Crabbe's, which was said to be like a grunt. So how could Crabbe's voice be a grunt when he was twelve but then soft when he was seventeen or eighteen? It also says that Harry had hardly ever heard Crabbe speak before, but he would have heard his voice a lot when Ron spoke after taking the Polyjuice Potion in their second year at Hogwarts.
 * This is probably due to Crabbe's voice having not yet broken at age 12, but having definitely broken five and a half years later; Crabbe's voice could have changed in ways other than just becoming deeper.
 * In chapter twenty-three, Narcissa says that Draco "is home for his Easter holidays." In chapter twenty-four, the sun is described as rising at Shell Cottage in Cornwall. But shortly after this, Harry sees into Voldemort's mind at Hogsmeade, where it is "still dark, because it was so much farther north." But (in the absence of a significant longitude difference, as in this case) this sort of thing is only true between the Autumnal and Vernal Equinoxes; Easter occurs after the Vernal Equinox (e.g. on April 12 in 1998), in the other half of the year when sunrise is earlier the further north one goes, thus it should not have been dark at Hogwarts when Harry saw into Voldemort's mind.
 * When Ron returns after having walked out on the other two, he informs them about the Taboo that has been placed on Voldemort's name, and that saying his name would break any protective enchantment placed on and around the person, and that this was how the Death Eaters had found them so easily on Tottenham Road. This does hold true, when the trio are later captured by a gang of Snatchers. However, this Taboo fails to come into effect when they say Voldemort's name at Grimmauld Place, as the Fidelus Charm continues to hold.
 * However, the Death Eaters do patrol outside of it, but due to the fact that they do not know that the Headquarters for the Order of the Phoenix are located at Number 12 Grimmauld Place, they can not access it. They could be aware that Harry, Ron, and Hermione are at Number 12, as it is not there, and the disturbance comes from the area, but because they do not know that the Headquarters is located there, they cannot cause it to appear. However, once Yaxley is brought within the enchantment, there is no reason to suspect that, were they to stun him and obliviate him, they could not keep hiding there.
 * Harry's worries about the Trace are unfounded. In A Place To Hide, he never used magic to clue in anybody as to his location: it was only the fact that they said Voldemort's name. No one used magic until after the Death Eaters found them. (Technically, Hermione used Apparition to get them there and Ron and Harry were side-along.) Later in the book Harry comments that it would be very hard to be on the run if he could not perform magic, implying that a person is not traceable merely because they have the Trace, they would have to perform magic to cause the spell to make them able to be located.
 * Furthermore, if the Trace can detect underage magic for a specific individual, than that means that there would be no question of who cast a spell. This would mean that Dobby's use of magic in Chamber of Secrets and Tom Riddle's in Half-Blood Prince would not have been attributed to Harry and Morfin Gaunt respectively.
 * This cannot be true as in a previous book it says that the Ministry can only detect magic and depends on the parents to enforce the rule.
 * In Half-Blood Prince, the Death Eaters enter Hogwarts via the Room of Hidden Things, yet a year later Voldemort is certain that no one else knows of the room's existence.
 * However, he may have not known that the Vanishing Cabinet was in there, just that it was somewhere inside Hogwarts.
 * When Lupin comes to visit the trio at Grimmauld Place he states, "I would have been here sooner, but it took 3 days to shake the Death Eaters that were tailing me..." Just a few sentences later while speaking of how the Death Eaters located the trio in the Cafe, that it is "Impossible to trace someone who Apparates, unless they grab hold of you..." This implies that Lupin either could not Apparate from his house to Grimmauld Place or that the Death Eaters in question were touching him for 3 days. Unlikely in both cases.
 * However, it is possible to watch where someone Apparates to, considering Pius Thicknesse making it illegal to Apparate to and from 4 Privet Drive, which would force them to fly. It never says they could not Apparate if they wanted to, which means they could, but due to a) the protective enchantments on the safe-houses and b) this potential watch, they must have been forced to use brooms and were given no alternative some way.
 * When discussing Godric's Hollow, Harry implies he has never read A History of Magic, and indeed may have only opened it once when he bought it. However, he spent a considerable amount of time flipping through it and his other textbooks in Philosopher's Stone while waiting for 1 September to arrive, and read the section on witch burnings for homework in Prisoner of Azkaban.
 * He could have simply lost interest in it, considering Binns is described as making even the most violent Giant Wars seem dull and uninteresting.
 * However he did get the name "Hedwig" from A History of Magic so presumably he must have done more than skim-read it, as it is unlikely he would pick the first name to appear in the book for his pet, he would have put some consideration into her name.
 * In the second chapter, Daedalus tells Harry that plans have changed regarding Moody taking him out of the house by side-along apparation. However, after making it to the Burrow, Lupin demands that Harry prove he is the real Harry since someone knew they were going to move that night. Harry did not know the new plans so he could not have leaked them. Finally, in Goblet of Fire, it was stated that Crouch Jr kept Moody alive, in part, to get his hair, implying the polyjuice potion needs real hair from the source and not from the clone. If that is so, no one would have changed into Harry.
 * In chapter 17 Harry gets bitten by Nagini. Hermione cleans the wound and puts dittany on it. But before, in book 5, Mr Weasley gets bitten by Nagini and he has to be in St Mungo's as they do not know how to treat his bites and they can't get them to close up.
 * In chapter 27 Harry drips dittany through the singed hole in his jeans to the angry burn beneath. But he has just got changed, so he shouldn't be wearing his singed jeans anymore.
 * In chapter 30, when talking about how to evacuate the students, Harry reassured Prof. McGonagall "they won't be interested in anyone who's Disapparating out of the Hog's Head." Harry, however, already knows that Disapparating within the bounds of Hogsmeade is impossible, having tried when he first got there and being told by Aberforth. Also, most of the students who are evacuating are not old enough to have learned how to disapparate.
 * During night there was a curfew. The likelihood is that the apparition restrictions set in at the same time. They could possibly have been able to disapparate from Hogsmeade during daytime. The young students could have been taken side along by some of the older students.