Still pictures that move
Picnic blanket
Move your eyes around the picture. Are the rows straight?
Yes, every one, though they seem to bend into waves and drift.
Why? The little light and dark corners on each check tilt the edges a bit, like the twisted checkerboard, and the same dark-and-light delay as the drifting circles makes them seem to slide.
Picture: Cmglee, CC BY-SA 4.0 · Wikipedia(opens in a new tab)