Try this with your friends at work:
1. Sit in your chair and extend your right leg
2. Start making it do clockwise circles
3. After you get the hang of it, trace the number six in the air with your right hand
I bet your leg switched directions, right? (If not, try it again) You can thank [Roger Sperry](http://en.wikipedia.org/wiki/Roger_Wolcott_Sperry) for explaining how this one works.