Actually it's just science... and you can do it, too!
Physicist David Willey from the University of Pittsburgh physics department and 20/20 anchor John Stossel show how it's done:
Willey laid out 165 feet of lumber and set it aflame. As [they] waited for the lumber to turn into hot coals, he said that anyone can "fire-walk" in their bare feet, provided they keep moving, because when you touch burning wood or charcoal, the heat doesn't go instantly to your feet. You'd be burned if you walk on hot metal, but wood and charcoal don't conduct heat very well.Hot coals can (slowly) roast a marshmallow and burn at a temperature of approximately 1000 degrees F. But it's a poor thermal conductor, so it takes a while to "conduct" (move) the heat from itself to whatever it's touching. If you keep walking at an even pace on the coals your feet won't keep in contact with any coal long enough to burn them! Plus, and this is pure speculation, the fact that the skin on your feet is so thick probably delays the heat transfer as well.
You're not so scary anymore, are ya?