Scientists in the 1930's first sought explanations for how participants of the ritual paced unscathed. The University of London's Council for Physical Research found that the witchcraft was in the wood, rather than religious faith and supernatural powers.

Traditional fire-walking paths are made of wood, left to burn into smoldering coals. The coals can reach high temperatures. Most fire-walks occur on coals that measure about 1,000 degrees Fahrenheit.

Willey once walked on 1,800-degree coals.

People survive because only a small amount of heat transfers from the glowing wood to the souls of their feet.

"Even if it's on fire, wood doesn't get that hot," Willey said. "It's still a lousy conductor."

Conduction is one way that heat travels from one material to the next. Vibrating molecules of a hot material collide with more calm molecules of a cooler object, and transfer energy. The low thermal conductivity of wood means that heat stays trapped in the coals, transferring little heat to the feet.

A layer of ash on the top of the flaming path helps to further insulate the heat of the coals.