Prince Rupert's drop
noun
a glass bead in the shape of a teardrop, a by-product of the glass-making process, formed by molten glass falling into water. The body of the drop can withstand great force, for example a hammer blow, but the whole will explode if the tail is nipped or the surface scored
Word Origin for Prince Rupert's drop
C17: thought to have been introduced to England by Prince Rupert, the German-born nephew of Charles I of England