Sit with a blank white wall to your right. Have a friend sit facing you. Hold up a hand mirror between you, positioned so that your left eye sees your friend’s face and your right eye sees a reflection of the wall. Now sweep your hand in a circular motion across the wall. Your friend’s face will disappear except for his eyes and mouth, like the Cheshire Cat in Alice in Wonderland.

This is worth the trouble to try, as the effect is startling. Your friend’s disembodied eyes may float before you for five seconds if he doesn’t blink or smile.