The "hot ice" effect (sodium acetate trihydrate)

There are many "hot ice" videos on YouTube.  The best textual information I've found is from NurdRage: v"...hot ice is simply sodium acetate trihydrate that's been heated above its melting point of 58 Celsius so it liquefies, and then carefully cooled below it's melting point so it’s supercooled. The dramatic freezing is initiated by a disturbance such as touch or a solid piece of another substance with the right molecular arrangement."

Here's one place to buy the material.