Rope Magic - Ball balanced on rope

The Effect: A 1m, 1m and a half of rope is held tightly between the
performer’s hands. The performer proceeds to balance a ball on the rope and mystically the ball rolls from one end of the rope to the other.

The Secret: A thin piece of black thread almost as long as the
rope is used to build a track for the ball to roll on. Tie both ends of the thread near the ends of the rope leaving just a little slack. Facing the audience, hold the rope tight with both hands at opposite ends. The black thread should be behind the rope. Insert your thumbs between the rope and the thread to spread them apart from each other, this is what creates the secret track. Now your ball can be rolled back and forth on a single piece of rope.

Advice: Wear black clothing in order to conceal the black thread. Use a ping-pong ball for an easier performance. You might try it with a tennis ball, but make sure the black thread is sturdy enough.