This is a very effective trick that’s in the mental category.
The performer shows a necklace of Pop-Out Beads, which can be separated or joined at any place by merely popping the beads out or in of their sockets. A spectator selects any number between one and forty-nine as the necklace has 50 beads. There is no force.
The necklace is broken into a chain, and the spectator holds one end of the chain, while the performer holds the opposite end. The spectator is asked to tug at the chain, and it breaks, leaving him with the exact number of beads which he selected!
The effect can be immediately and indefinitely repeated with different spectators, and different numbers.