You ask for the loan of a bill. Any bill, any denomination. You display a small metal disc and explain that it is made of an unidentifiable material that you found while visiting what was rumored to be the site of a UFO crash! As you begin to rub the disc across the bill, it suddenly appears to melt halfway through! This is a startling and visual effect. To finish, you cause the disc to actally pop right through the bill and into the spectator's waiting hands.