Its also possible to replicate the 'supercooling' effect with other mixtures of liquid - for example beer, (which although I have done myself, this video from mythbusters is a better shot concept) which whilst it might typically contain about 4-5% alcohol by volume, plus dissolved carbon dioxide and certain other compounds can still be chilled to a point below its regular/expected freezing point & instantly frozen. It's a little trickier to get right though as it needs to be slightly colder than water alone due to the alcohol and other compounds present. Makes a neat party trick though!