Gervase is staring at the blades of his ceiling fan, searching for inspiration for a paper that he is writing. When he turns off the fan, he is very surprised that the blades appear to be rotating in the opposite direction. You could reassure Gervase that he is not hallucinating from being overworked by telling him about:

Question

Quizplus · Accepted Answer

Motion after-effects occur when, after looking at a moving object for a while and then looking away, stationary objects appear to move in the opposite direction. This explains why the fan blades seem to rotate in the opposite direction when stopped.

Gervase Is Staring at the Blades of His Ceiling Fan