This is so cool. I was just clicking links and found this one. I'd never heard of Prince Rupert's Drop before this, but it's a damn cool little structure.

It's created by dropping molten glass into cool water. It hardens into a tadpole form with a long twisting tail. You can hit the thick part of the glass with a hammer, and it wont break. However, if you even slightly nick the tail, it explodes.

Watch it explode @ 130,000 FPS.

Mystery of Prince Rupert's Drop at 130,000 fps