Waterfall illusion: the science behind why still objects sometime appear to move

Humans are fascinated by visual illusions, which occur when there is a mismatch between the pattern of light that falls on the retina, and what we perceive. Before books, films, and the internet allowed illusions to be shared widely, people were captivated by illusions in nature. Indeed, it is here that the long history of the study of illusions begins. Both Aristotle and Lucretius described motion illusions following observation of flowing water. Aristotle observed pebbles beneath flowing wate