Coin Bite Trick
Effect: The magician borrows a coin from the spectator and is seen to take a bite out of the coin.
Preparation: Take a quarter and file one side of it down so it looks like someone has bitten a chunk of it off.
Method: Approach a spectator and ask them to borrow a quarter.
You already have the gimmicked quarter in palm position between your thumb and forefinger of your right hand. Take the quarter from the spectator and quietly move your finger and thumb and switch the coins.
Their coin is now slid to the back of your finger.
Pretend to be biting and tearing of a section of what is now your gimmicked coin and eventually tug it free of your mouth to show the spectator who should look amazed.
You can learn all about coin magic in Modern Coin Magic: 116 Coin Sleights and 236 Coin Tricks which is highly recommended reading and is an excellent way to learn.