Odd Ball by Marc Oberon

A selection of small white balls and one single black ball are shown to the audience. They are dropped singly into an opaque bag, which is then shaken by a spectator to ensure they are well mixed.

One by one a group of spectators each take a ball from the bag, keeping it concealed at all times in their hand.

Despite the thorough mixing and random distribution of the balls, you can instantly tell who holds the black ball.