We've all heard ice crack in water, because the water is warmer than the ice. What if ice cubes were dropped in something colder than they are? Take a look at a slow-motion video of an ice cube being dropped in liquid nitrogen.
Ice cracks up in water because its rigidity goes head-to-head with its conductivity. The fact that heat doesn't travel well through the ice means some parts warm up much faster than others. In the case of an ice cube being dropped into water, the outside warms up faster than the inside. The heat causes the ice on the outside of the cube to expand, and the ice on the inside of the cube can't keep up, either with the temperature change or with the expansion. The ice cracks.
If someone were to drop the ice cube in cold liquid - like the liquid nitrogen in the video above - the reverse happens. The outside of the cube contracts, and shatters itself on its own insides. And it looks really cool.
[Via Periodic Videos.]