The original trick (invented by Lubor Fiedler in the early 1960's) was for a coin to penetrate a rubber sheet. Since then, many other ideas have been created using this principle. But the most popular still is to have a coin is sitting on top of rubber sheet that's stretched over the mouth of a glass. A spectator is asked to simply push the coin, as this is done, the coin incredibly and instantly penetrates the rubber sheet and falls into the glass. Everything is left with the spectators for full examination.