The Leidenfrost effect is a phenomenon of physics in which a liquid, close to a surface that is significantly hotter than the liquid’s boiling point, produces an insulating vapor layer that keeps the liquid from boiling rapidly.
This is most commonly seen when cooking, when a few drops of water are sprinkled onto a hot pan. If the pan’s temperature is at or above the Leidenfrost point (approx. 193 °C or 379 °F), the water will skitter across the pan and take longer to evaporate than in a cooler pan.
On commenter on Reddit noted how the phenomenon used to freak him out as a child. His parents owned a diner and his mom cooked. “She would grab a handful of cut french fries from a bucket full of potatoes and water, shake them once, and then stick her hand and the french fries in the fryer – never getting burnt.”
The effect has also been used in some potentially even more dangerous demonstrations, such as the one below. It is responsible for the ability of a person to quickly dip a wet hand or finger in molten lead or blow out a mouthful of liquid nitrogen without injury. The latter is potentially lethal though, particularly should one accidentally swallow the liquid nitrogen. So don’t try this at home!
Molten lead does not glow red by the way…