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What: This is the second optical toy on this website that demonstrates this effect. Even though the other one uses spirals, they produce a similar effect, though it's a bit more dizzying. A motion after - effect takes place when you watch a moving pattern for some time and then start looking at something else.

How To: Stare at the center for a little while, and then look at something nearby, whether it's the wall, a piece of art, or your own hands. You should notice them seem to bulge and expand, or shrink and contract. You can also close one eye and experience it with, well, half of your field of vision!

Explain It: Once again, it's difficult to explain clearly, but here's a great account described by Aristotle himself! "Also, when persons turn away from looking at objects in motion, e.g. rivers, and especially those which flow very rapidly, they find that the visual stimulations still present themselves, for the things really at rest are then seen moving." Ultimately, it is thought that your neurons are encoding a specific movement and reduce their responses as you're exposed to a constantly moving stimulus over time. When you look away, the neurons that are encoding the opposite movement become more active, and that's why you see the reverse.