With your arms down the side of your body, stand next to a wall with your left shoulder, outside of the left arm and side of the left foot touching the wall.
Now, without breaking contact with the wall, try to lift your right foot.
Go on, try it!
(If you want, you can give it a shot from the other side around as well).
Even I didn't believe it at first, but this simple sounding act is a physical impossibility!!