You set this trick soap bar up by following the instructions that come with it and when someone lifts it up to use it, it makes a loud bang scaring the living daylights out of your victim! The device uses plastic caps (not supplied) to produce the bang. The person who sets it off won't know what has happened until you tell them that they've been had! They come with instructions on the back of the packaging.
We also sell the caps to use with this product.