Don't just stick your hand in molten lead. This can be done by dipping your hand in water right before dipping it into the lead, but you have to really know what you're doing.

The technique as summarized by Redditors:

By lightly covering your fingers with water, the molten lead evaporates the water which creates a sort of vapor forcefield which prevents the lead from actually touching your fingers. Too little water and there's no forcefield. Too much water and you risk solidifying super fucking hot lead to your fingers. Don't try it at home. This is also how coal walking works (usually.) Sweat/dew from grass coats the foot before walking on coals.

TL;DR: Leidenfrost effect -- hand hotter than boiling point of liquid + some liquid = layer of vapor between hand and liquid that protects hand.

For more: http://en.wikipedia.org/wiki/Leidenfrost_effect

Same principle here: http://www.popsci.com/diy/article/2010-08/cool-hand-theo

Similar effect with liquid nitrogen at 165s: