Physics lessons I learned on my vacation

If you heat water in a microwave, it is possible to overheat, or "superheat" it, in such a way that it goes past its boiling point. The water will appear innocently flat to the eye, but the introduction of a cooler substance or object (say, a baby's bottle) will trigger a "flash boil". The boiling water will then explode out of the container in a rain of scalding liquid. Quite spectacular, really.

This would be why I am missing a patch of skin on the back of my thumb right now. Ow. But hey, at least the baby didn't get hurt; he just cried because my screaming startled him.