Superman trick Roy Kueppers

The Magician approaches an unknowing spectator and asks, Do you have a quarter on you today, Ma'am? The spectator proceeds to look for change in her pocket. The Magician then prompts, Could you please sign the coin for me before I take it from you. (The coin does not need to be signed, but it adds to the effect's finale.) At this point, the Magician takes the coin, holding it in view of the spectator, and says, I'm going to try something here ... You know what? You may be able to do the same as I do. Do you have another quarter? The spectator reaches into her pocket and retrieves another coin. The Magician, holds the signed, borrowed coin at the fingertips, and begins to rub the coin, saying, Rub your coin like me. Can you see mine starting to bend? The Magician finishes showing the bent coin, and immediately gives the coin to the spectator as a souvenir. The coin can now be fully examined.