Here’s an interesting optical illusion. Depending upon how your brain interprets the sense data from your eyes the dancer in this video either spins clockwise or anti-clockwise.

If you see it change direction, rewind and watch it a again, you’ll find it doesn’t change at the same time. Apparently the direction you see it move in depends on which of your brain hemisphere is more dominant. I find that if i defocus my eyes I can sometimes make the figure change direction.

The world you see out there… is all in your head.