Crack an egg into liquid nitrogen and it does not freeze on contact. It floats. Liquid nitrogen boils at 77 K. The egg arrives roughly 216 K above that, far beyond the threshold where boiling stays orderly, so the first layer of nitrogen flashes to gas and builds a vapour film before any liquid touches the shell contents. This is the Leidenfrost regime, identified by Johann Gottlob Leidenfrost in 1756, and the film is an excellent insulator. Heat flux collapses by roughly two orders of magnitude against the nucleate boiling a merely cold surface would deliver. The egg skates on its own exhaust. The energy accounting underneath: - Nitrogen expands approximately 690 times from liquid to room-temperature gas, so the violent churn is a very small mass becoming a very large volume. - Its latent heat of vaporisation is only 199 kJ/kg against water at 2,260 kJ/kg, meaning it carries heat away poorly per unit mass and boils off quickly. - Dragging a 50 g egg from 293 K to 77 K costs on the ...