The Self-propelled Ball

Effect: A ball rolls across the table until you tell it to stop.

Secret: Under the table cloth is a small ring attached to a length of strong thread. The thread runs across the table to where your secret assistant is sitting. A small ball is placed on the table. It must go into the concealed ring. On your word of command your assistant pulls on the thread and the ball moves. You then pick up the ball and hand it to a spectator. As you are doing this, your assistant pulls the ring from beneath the cloth and hides it.