Tongue-Tying Curse

Tongue-Tying Curse has no known incantation.

It binds the target's tongue to keep him or her from talking about some specific subject.

Uses
Arthur Weasley said that Mad-Eye Moody had set up a couple of curses at number twelve, Grimmauld Place in case Snape returned there. The curses were to both "keep him out and bind his tongue if he tried to talk about the place" in 1997.

Harry, Ron, and Hermione were affected by this upon their arrival at number twelve, Grimmauld Place. Something whooshed over them like cold air, causing their tongues to curl backward on themselves, making it impossible for them to speak, though their tongues soon unravelled again. It was unpleasant, and afterwards Ron made retching noises and (with Hermione) stammered for a little while.