Toss a few droplets of water in a hot pan and they seem to come alive, skittering to and fro as if trying to escape. Try the same thing with balls of hydrogel, and they actually could break free. The spheres bounce animatedly about a hot pan, emitting a piercing, shrieking noise as they do so.
Both tricks are due to something called the Leidenfrost effect, which describes the instantaneous vaporization that occurs when water touches a hot surface. If enough steam is produced, it can be en