http://feedproxy.google.com/~r/boingboing/iBag/~3/7H_gk6HRMmY/story01.htm

http://boingboing.net/?p=222980

Prince Rupert's Drops are unusual glass objects made by dripping molten glass into water. The exterior is very compressed while the interior is under great tension. You can hammer on the head of a drop and it won't break but if you barely wiggle the tail, the whole thing explosively shatters. It's particularly amazing in super-slow motion.