Grasp the rings on both sides of the mirror.
Tilt your head to the left to look in the mirror. The mirror image of your left hand is covering your view of your right hand.
Without changing the position of your head, move the disc on the right.
How does it work
The movement of the disc causes surprise and confusion because our brain expected to see motion but did not.
The idea for this device comes from the Portland Science Center in the United States of America.