Sectumsempra

"Blood spurted from Malfoy's face and chest as though he had been slashed with an invisible sword. He staggered backward and collapsed onto the waterlogged floor with a great splash, his wand falling from his limp right hand. Slipping and staggering, Harry got to his feet and plunged toward Malfoy, whose face was now shining scarlet, his white hands scrabbling at his blood-soaked chest."

- Description

Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, likely including the Marauders and it became one of his specialties.

Creation
"You dare use my own spells against me, Potter? It was I who invented them ~ I, the Half-Blood Prince!"

- Professor Snape telling Harry Potter that he is the prince



The curse was invented by Severus Snape and recorded during his time as a student at Hogwarts, for use in retaliation against his enemies such as the Marauders. He recorded it in his N.E.W.T.-level Potions textbook and used it enough to allow Remus Lupin to recognise it as one of his signature spells. It's possible that he cast it against James Potter during their fifth year at Hogwarts after the Marauders publicly humiliated him, however this is unlikely since effects were not as extreme as they were when the spell was used against Draco Malfoy and George Weasley.

=== 1996-1997 school year===

Many years later, in the 1996–1997 school year, Harry Potter came into the possession of Snape's textbook, and learned the incantation. Without knowing its effects at the time and believing that the "Half-Blood Prince" (Snape's nickname signed into the book) merely copied it as a note of reference, Harry became interested in trying it, thinking it would have some hilarious effects similar to Levicorpus and other spells found within the same book.



Harry considered using it against Cormac McLaggen for annoying him, though it was not until he confronted Draco Malfoy in Moaning Myrtle's Bathroom that he utilised it, seriously wounding Malfoy. Snape intervened to heal Draco, and having realised that Harry got a hold of the old textbook, he punished Harry with a multitude of detentions; Snape did not turn Harry in for a deeper punishment for fear of exposing himself to be the inventor of the curse. Harry, despite disliking Malfoy, did not truly want to harm Malfoy to such an extent, and was both horrified and guilt-ridden by using the curse against him. Professor McGonagall considered Harry to be lucky not to have been expelled for such an act, and she full-heartedly supported the detentions, while Pansy Parkinson wasted no time in vilifying Harry far and wide.

During Harry's hunt for a Horcrux, he accidentally attracted the attention of an army of Inferi, and in an attempt to stop them he used many spells including Sectumsempra. However, this merely slashed their unfeeling flesh, creating no serious impediment to their approach. Later the same night, when Snape killed Dumbledore, Harry attempted this curse against him, only for Snape to negate it and angrily confront Harry revealing that he was the inventor.

1997-1998 school year
The next year, during the Battle of the Seven Potters, Snape attempted to use this curse to sever the hand of a fellow Death Eater, but due to a slip, he accidentally cut off George Weasley's left ear instead. The Order of the Phoenix was not able to regrow the wound by any means due to the nature of Dark Arts, though it is unclear whether this is because doing so is completely impossible or because they did not know how to counter the spell.

Nature
A rather dangerous curse, when the incantation is uttered its effect is the equivalent of an invisible sword; it is used to slash the victim from a distance, causing rather deep wounds. The slash follows the user's wand movements. Due to the depths of the cut, the victims run the risk of dying from blood loss if treatment is not applied in time, if the wounds are not instantly fatal.

Counter and treatment
Wounds inflicted by this spell can be cured by the song-like incantation Vulnera Sanentur; the first usage eases the blood flow, the second causes the wounds to knit and the third removes the worst effects of the curse. The victim would still require medical treatment, and if dittany is applied immediately, scarring can still be avoided.

Though the aforementioned healing spell may heal the wounds and essence of dittany may prevent scars, any body parts that have been severed by this curse cannot be grown back (a trait of dark magic's permanent effects), as demonstrated by George Weasley when he lost his left ear to the spell.

Known practitioners

 * Harry Potter
 * Severus Snape
 * Lord Voldemort

Etymology
Sectumsempra derives from the Latin sectum, "having been cut" (comparable to the English word "section" or "segmented"), and possibly semper, "always." It can be translated as "always cutting" or "sever forever", the latter being a pun on Snape's first name, Severus, as well as indicating that severed body parts cannot be regrown.

Behind the scenes

 * It is unknown when Snape invented this spell as according to Sirius Black, Snape "knew more curses when he arrived at school than half the kids in seventh year."
 * Snape's invention of Sectrasumpra was not likely a secret as Remus Lupin is able to recognise it during the Battle of the Seven Potters.
 * In the films, Sectumsempra appears as a small flash of white light launched forward like many spells, which causes a cut when it strikes the target.
 * In, Harry uses Sectumsempra on Malfoy only to find out the spell has, apparently, painlessly sliced him in half.
 * This curse's effect is similar to the Severing Charm, except it is used for more malicious intent and causes more slash-like wounds.

Notes and references
Sectumsempra Sectumsempra Sektumsempra Сектумсемпра Σεκτουμσέμπρα Sectumsempra pt-br:Sectumsempra