Still pictures that move
Enigma illusion
Look at the purple rings. Do you see anything moving in them?
Many people see a flicker streaming round the rings, though they are plain purple.
Why? Scientists still argue: it may come from the rays, or from your eyes’ tiny jumps that never stop, even when you stare. Isia Leviant made it in 1981.
Picture: Drawn by Science Playground, after Isia Leviant