Japanese puzzle maven Kobon Fujimura devised this mind-reading trick. Ask a friend to look at his analog watch and mentally choose one of the hour numbers. Tell him, “I’m going to point to various numbers on the face of your watch with a pencil. As I do so, count silently, starting with the number after the one you’ve chosen. For example, if you’ve chosen 7, start counting with 8. When we reach 20, say, ‘Stop.'”
Point to any seven numbers at random, pretending to concentrate deeply. Then point to 12, then 11, 10, and so on counterclockwise around the dial. When your friend tells you to stop, you’ll be pointing to the number he had chosen.