What would happen if you stick your hand in a pool of liquid nitrogen? Would your hand freeze to death? Would it harden to an unnatural state? Would it shatter as soon as you touched something? Well, real life isn't like the movies (i.e. Demolition Man), so believe it or not, your hand would be safe, thanks to a little known phenomenon called the Leidenfrost effect.
In this science video tutorial from Nurd Rage, he demonstrates the Leidenfrost Effect with liquid nitrogen—and his own hand!
Pretty amazing, huh? He sticks his hand (momentarily) directly into liquid nitrogen and doesn't suffer any injuries—thanks to the Leidenfrost effect. And not only does he do it once, but twice—the first video is a little fast, but the second video (below) is redone in slow motion, for a better understanding. Watch both to fully grasp the phenomenon and learn the steps to doing it yourself.
The Leidenfrost effect is the formation of a gas barrier between a hot surface and a boiling liquid if the temperature difference is great enough. This gas barrier greatly slows the heat transfer between the two and allows the liquid to last longer and consequently the hot surface to remain hot longer. This effect can be seen in a frying pan as it's being heated. At first the water quickly boils as it's dropped in but at a hot enough temperature the Leidenfrost effect takes over and makes the water skate around the surface lasting a very long time.
Liquid nitrogen vs. a room temperature object will also exhibit the effect preventing it from instantly freezing the object... such as a hand.