interference pattens .. when I was a kid I used to walk home along the edge of an old railway and on sunny days the metal fencing along the path produced a similar effect, I used to close my eyes and walk as fast as i dared seeing a stroboscopic red/green/red/green patterning on my eyelids as i did so..
I am a fan of optical illusions. Just last night I was watching on National Geographic two balls running in an X pattern. One pass without noise so you see up-left to down-right and up-right to down-left. Adding a noise just when they overlap, you actually see one going up-left to center to down left and the second up-right to center to down-right. So, I don't trust my eyes