This is an example of supercooling – the process by which a very pure liquid is chilled to a temperature just below its usual freezing point without actually making the jump to its solid state. Bottled water is perfect for this, especially the kind that’s been purified via reverse osmosis, a process that strips water of all its particulates. This particulates can act as “seed crystals,” or “nuclei,” to which a liquid phase on the cusp of becoming solid can attach, and crystalize around. In this video, a seed crystal is introduced in the form of a cube of already-frozen water. As soon as it’s introduced, the liquid phase rapidly crystallizes and attaches to the solid one, kicking off a chain reaction of ice-formation.