Staying balanced on those big blow-up exercise balls in Pilates is tough enough just doing basic moves. For the life of me, I can't lay on one of those balls without getting a head rush.
Check out this ripped Men's Health hunk doing one foot push-ups using two of the balls, one for his feet and the other for his hands. Oh yes people! His feet never touch the ground. I am floored by this guy's strength and balance. Don't try this at home unless of course you have super Heroes or 4400 ability.