Prince Rupert’s drops are made by dripping molten glass into cold water, which causes it to solidify into a tadpole-shaped droplet with a long, thin tail. They have internally very high residual stresses, giving rise to properties such as the ability to withstand a blow from a hammer or a bullet, while exhibiting explosive disintegration if the tail end is even slightly damaged. The drops are named after Prince Rupert of the Rhine, who brought them to England in 1660, although they were reportedly being produced in the Netherlands earlier in the 17th century and had probably been known to glassmakers for much longer.
https://en.wikipedia.org/wiki/Prince_Rupert%27s_drop