The
coolest thing about
liquid nitrogen (apart from making
ice-cream) is to stick your hand
deep in a
vat of it for about 2 seconds, then
remove. Instead of getting a
frozen hand that you can
smash on a
table, this happens...
As your hand goes in, the temperature of your hand (which is much greater than the boiling point of liquid nitrogen) causes the liquid nitrogen next to it to vapourise. There then exists a small layer of Nitrogen gas around your hand, which is warmed up by your hand, and the vapour pressure keeps the liquid nitrogen from touching you. Of course given time, the heat in your hand would drop low enough so that you would want to remove it "pretty quick" :).
What this boils down to is "Putting your hand in liquid nitrogen feels funny!" :P It's cool, and I'm addicted.