What's the science behind fire-walking?

There's no trick to it necessarily. It's not entirely what it looks like. Basically there are three components. The first thing to consider is that when you're walking across fire, understandably, you do it a bit quickly. So you're actually minimising the time that any particular part of your body is in contact with the fire. This is the same reason that lizards scoot about in the desert on hot rocks. The quicker they move, the less they're going to burn themselves. There are two other things: the fires are lit and left to burn until they become like a barbecue. The top layer of that is ash. Ash is actually a pretty good insulator against the direct heat underneath. So you can feel the heat above it but the burning heat won't get through so much. Also carbon is the component of the coals. Carbon is a very poor conductor of heat so the burning at the bottom of the fire pit won't come up so much. So it's not as hot as it looks and also you go across it very fast.There is another theory that because you're a bit nervous, just as you would get sweaty hands, your feet sweat a bit and you effectively surf across the top of the coals on a cushion of steam which also helps to keep the temperature down.