A magician sat at a table in front of a group of schoolchildren. He threw a ball up in the air a few times, but before his last throw, he secretly let the ball fall into his lap. Then he continued to throw an imaginary ball up in the air. Surprisingly, more than half the children claimed to have seen an illusory ball, or ghost ball.

The illusion relies on misdirecting the audience's expectations to anticipate you throwing the ball for real.

In the vanishing ball illusion, a study found that when the magician pretends to throw the ball in the air, and his gaze follows the imaginary trajectory of the ball, almost two-thirds of the participants will be convinced that they had seen the ball move up. If his gaze did not follow the imaginary ball, the illusion was far less effective.

This illustrates that the illusion is mostly driven by expectations. Our eyes find it difficult to track fast-moving objects. Looking at the ball is only possible when we can predict where it will be in the future.