Perform this for a group of people. Pick five pennies with different dates on them. Place the pennies in a hat and ask one of your friends to pick a penny and look at the date, but not tell what it is. Then, let all your friends pass the penny around to look at the date. After everyone has seen it, quickly put the penny back into the hat and shake up the pennies. Magician reaches into the hat and pulls out the chosen penny without even seeing it.
The secret? The Magician knows which penny was chosen because copper absorbs heat, so the penny everyone has handled will be warm.