Nonverbal spell

"Your adversary has no warning about what kind of magic you are about to perform, which gives you a split-second advantage."

- Hermione Granger on the advantages of nonverbal magic

A nonverbal spell is a spell which is performed without saying the incantation out loud. Performing spells nonverbally is very difficult and requires a good deal of practice, as it requires concentration and mental discipline alone. Hogwarts School of Witchcraft and Wizardry begins teaching nonverbal magic to students in their sixth year in Defence Against the Dark Arts, Charms, and Transfiguration. Harry Potter noted that several students in his class looked "liked they had received an overdose in U-No-Poo", a substance that causes constipation, while attempting nonverbal spells.

Some spells, such as Levicorpus, are easier to perform nonverbally than others. Most spells, however, seem to be less effective than normal when the incantation is not said. For example, the unnamed curse that critically injured Hermione Granger during the Battle of the Department of Mysteries might have been fatal had Antonin Dolohov not been silenced when he used it, according to Hogwarts nurse Poppy Pomfrey.

The first person in Harry Potter's class to be able to perform nonverbal spells was Hermione Granger, who cast the Shield Charm without speaking. She continually used nonverbal spells in Defence Against the Dark Arts, Charms, Potions, and Transfiguration. Harry himself found nonverbal magic very difficult to do, though he was eventually able to cast Levicorpus, a spell meant for nonverbal use.

Known Practitioners
The following is a list of wizards and witches known to have nonverbally performed spells that are usually performed with an incantation.
 * Antonin Dolohov
 * Albus Dumbledore
 * Filius Flitwick
 * Hermione Granger
 * Remus Lupin
 * Draco Malfoy
 * Minerva McGonagall
 * Severus Snape
 * Lord Voldemort