One of the best and most popular “puzzelboxen” ever made.

Effect: The performer shows a wooden box that appears to be completely sealed on all sides. A transparent plastic window on top reveals the box’s contents. The box is thoroughly examined by the audience, and there seems to be no other way to get inside than by breaking it open!
A bill is borrowed and folded in half, or smaller, so that it fits inside the box. The bill is signed by the spectator so that he can identify it. It is then placed over the transparent window on top of the box.
The box is now briefly tilted out of the spectator’s view and then handed to him. He is surprised to find the bill sealed inside the box. He can see his signature through the transparent window.
The spectator is asked to remove the bill without breaking the box or tearing the plastic window. There is plenty of room for comedy at this stage…

Finally, the box is briefly put out of sight (behind your back, or under the table), and the bill is removed and handed to him.
Everything can be examined again.