A coin is pushed into the slot of the plastic disc where there are a number of small steel ball bearings. The coin easily pushes the steel ball bearings out of the way to enter the disc but when you try and remove the coin it is a completely different story as now the ball bearings prevent the coin from comng out of the disc unless you know the clever method to do so.
This will drive them crazy. It looks easy but try as they may the coin can not be removed. You take the disc back from the person and within a matter of seconds you are able to remove the coin!
Supplied with a quarter and operating instructions.