When a “stocky Italian air force lieutenant" named Raimondo Bucher agreed to dive 30 metres to the bottom of a lake on a bet, science dictated his lungs would collapse. Without the aid of an oxygen tank, it was thought the increasing weight of water would diminish the single breath of air he'd taken inside them. Which would have been a bummer, because there was 50,000 lira on the line.
So how did he not only survive, but succeed? And how can modern freedivers plunge over 100 metres into the depths, aided by nothing but a single breath? The key is a phenomenon named the 'mammalian dive reflex', which its discoverer, Per Scholander, dubbed "the master switch of life".
It turns out that contact with water lowers the human heart rate, which lengthens the amount of time we can spend underwater without oxygen. The TED Ideas blog has the full story of how cold water on your face can trigger a lot more than an abrupt start to the day.