In the old Warner Bros. cartoons a common scenario often involved the sweet and vulnerable Tweety Bird slipping some alum to the menacing Sylvester. This causes the cat's mouth to forcibly pucker and prevents him from being able to devour the "defenseless" canary.
In folk magic, this mineral is used in a somewhat similar fashion: Spells to "stop gossip" and to silence chatter often employ alum toward this end, causing the mouths of those who talk behind your back to "pucker" and close. Candles are rolled or dressed in alum powder to be burned for this purpose, and chunks of alum are carried in mojo bags.
Sold as curio only. Keep out of reach of children.