Rupert's drop \Ru"pert's drop`\
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}.
[1913 Webster]