|Muggles' Guide to Harry Potter - Magic|
|Features||Binds the tongue to the roof of the mouth, preventing speech|
|First Appearance||Harry Potter and the Half-Blood Prince|
The Langlock spell is one that prevents someone from speaking about something specific by binding their tongue to the roof of their mouth.
Harry finds this spell in the Potions text that belonged to the Half-Blood Prince. He uses it at one point in the story to silence Peeves, who is loudly commentating a fight between Dobby and Kreacher. We also guess that this is the spell left in the entrance to Number 12, Grimmauld Place by Mad-Eye Moody as part of the attempt to prevent Snape's entrance.