This is a fun, light-hearted post, unless you're my wife (I'll explain that momentarily). From here.

Do you see the dancer in the image below turning clockwise or anti-clockwise? If clockwise, then you use more of the right side of the brain, and vice versa. Note that most people see the dancer turning anti-clockwise.

Me? I saw the dancer turning clockwise. Then I sat and tried to see her moving anti-clockwise. I didn't succeed until I closed my left eye and then suddenly there she was, moving anti-clockwise, and I couldn't make her go back to moving clockwise, no matter which eye I closed. So I used my finger to trace the path of her outside foot across the screen, in a clockwise direction, and it snapped back to looking as though it moved clockwise.

That is the point at which my wife screamed and proclaimed it was just too damn freaky, refusing to look any longer because now she was seeing it go the opposite direction.

It was really creepy when I started seeing the dancer jump back and forth between clockwise and anti-clockwise movements. Ah, the brain, you wonderful, mysterious, awesome organ, you.