A small metal clicker/disk within a sealed pouch containing a clear, colorless liquid is clicked, and the liquid rapidly crystallizes into a solid mass and releases a large quantity of heat. If the solidified pouch is allowed to cool back to room temperature and then is reheated, it returns to its liquid state with its “recharged” latent heat available for release again when desired. In this activity, sodium acetate trihydrate melts (dissolves in its own water of hydration) when heated, and it remains stable as a supersaturated liquid solution at room temperature until it is disturbed by either clicking the metal disk (if done in a sealed pouch) or adding a seed crystal (if done in a test tube). Either the metal clicker or the seed crystal can be viewed loosely as a “catalyst” for accelerating the rate of the physical change.