Sprinkle water over a hot pan, and the droplets seem to roll across the pan's surface. Modernist Cuisine (via Eater) explains why this is so in the introduction to an amazing video of the Leidenfrost Effect slowed to 3,000 frames per second:
When a drop of liquid first contacts a surface that is much hotter than water's boiling point, an extremely thin layer of vapor forms under the drop. This layer of vapor suspends the drop slightly above the surface, creating the hovering effect. The vapor also acts as an insulation layer between the surface and liquid, keeping the liquid from rapidly boiling away. This fascinating occurrence is known as the Leidenfrost effect, named for the 18th-century German doctor and theologian who first described the phenomenon.
