Go to a mirror, and stand very close to it with your head up straight. Look carefully at your eyeballs, then slowly tip your head to one side. Your eyeballs rotate the opposite way to your head so they remain on the horizontal plane!

Not side-to-side, or up-and-down, but spin around the axis that goes through the pupils. I never knew eyes could do this!

Someone! Tell me what this phenomenon is called!

An addendum to this, months later... If you do this too much, your eyes may break free and begin spinning freely. Very freaky.

Just kidding.