Bouncing Venetian Blinds:

When you walk, does your head stay perfectly level with the ground? Not likely. So your eyes must be bobbing up and down. But the view you see before you is stable. Pretty clever brains, eh? I had the unsettling experience of walking towards a large window covered with open Venetian blinds. From a distance, the outdoor view through the blinds bobbed up and down alarmingly at each step, giving me an urge to walk more gently. At some point I got close enough and the outside view stabilized. Instead the blinds seemed to bounce up and down.