A spectators thought becomes engraved on your arm!
The Effect: The spectator select a card. No forces! Then he remembered that card. With the thought in mind, the spectator squeezes your wrist. Tightly. When the spectator releases, red marks appear on your arm where they were squeezing. These marks of blood under the skin then slowly, visually, clearly re-arrange themselves into the shape of the spectator's selection. Seeing is believing!