It's supercooled water. Basic principle is a liquid is reduced in temperature below its freezing point in absence of a seed crystal. As soon as it encouters a seed crystal, it freezes.
You can do it with a bottle of beer fairly easily. Seems to work best with corona for some reason, smooth bottle I would guess. Leave it in a freezer for about 3-4 hours. Then take it out and tap it. Some bubbles will form and act as seeds. Within a few seconds, the beer will be a solid block. There are dozens of videos of it on youtube. And yes this is serious alchol abuse.
http://www.youtube.com/watch?v=SfkHS...elated&search=