A tray, three cups and a ball are shown. The magician places the ball on the center of the tray and covers it with one of the cups. The remaining two cups are placed on each side of the hidden ball.
Now, in the classic three shell and pea con the cups are moved around. A spectator from the audience is asked to pick the cup concealing the ball. when the cup is lifted, the ball is not there. Another cup is lifted to show the location of the ball.
The ball con game is repeated as many times as you want using the same or different spectators. No matter how hard they try, the ball is never where they think it is.