rupert's drop

from The Century Dictionary.

• noun Same as detonating bulb (which see, under detonating).

from the GNU version of the Collaborative International Dictionary of English.

• A kind of glass drop with a long tail, made by dropping melted glass into water. It is remarkable for bursting into fragments when the surface is scratched or the tail broken; -- so called from Prince Rupert, nephew of Charles I., by whom they were first brought to England. Called also Rupert's ball, and glass tear.