Tongue-Tying Curse

From Harry Potter Wiki

Tongue-Tying Curse
Type:	Curse
Effect:	Binds target's tongue

Tongue-Tying Curse has no known incantation. It activates when a pre-determined subject is focused upon by the caster. This curse binds the target's tongue to keep him or her from talking about a specific subject.

In 1997, Alastor Moody set up curses to protect the Order of the Phoenix headquarters at 12 Grimmauld Place. One of these curses was this spell. It was so placed to prevent Severus Snape from revealing the area's location to Lord Voldemort, as the properties of the Fidelius Charm protecting the house created Snape a Secret-Keeper when Albus Dumbledore died. The curse was intended to both "keep him out and bind his tongue if he tried to talk about the place." It is unknown what would occur if Snape tried to write the location on paper, which would also have passed on the secret of the house's location.

Harry Potter, Ron Weasley, and Hermione Granger were affected by this curse when they sought refuge at 12 Grimmauld Place after fleeing Death Eaters in 1997. A sensation of cold air whooshed over them, causing their tongues to curl backwards, making it impossible for them to speak. Though their tongues soon unravelled again, Ron made retching noises an Hermione stammered for a while afterwards.