First, read this:
Prince Rupert’s Drops are a glass curiosity created by dripping hot molten glass into cold water. The glass cools into a tadpole-shaped droplet with a long, thin, tail. The water rapidly cools the molten glass on the outside of the drop, while the inner portion of the drop remains significantly hotter. When the glass on the inside eventually cools, it contracts inside the already-solid outer part. This contraction sets up very large compressive stresses on the surface, while the interior of the glass is placed under tension. It can be said to be a kind of tempered glass.
The very high stress within the drop gives rise to unusual qualities, such as the ability to withstand a blow from a hammer on the bulbous end without breaking, while the drops will disintegrate explosively if the tail end is even slightly damaged. When this happens, the large amount of potential energy stored in the drop’s crystalline structure is released, causing fractures to propagate through the material at very high speed.
Then, watch this: