Point your hands towards your chest. Cross your hands one over the other and interlock your fingers and then raise your knuckles. Now look at the index finger that is pointing to the left and wiggle it. Bet you move the wrong one.
From Making Light
While sitting in your chair, lift your right foot slightly off the ground and move it in clockwise circles. Now draw the numeral “6” in the air with your right hand. Your foot will involuntarily reverse direction.