Courtesy of a link at Dark Roasted Blend, I came across this video clip about a rather strange phenomenon. I found it fascinating. I recommend watching it in full-screen mode.
“There are more things in heaven and earth, Horatio . . . ” Indeed!
Peter
Back in the 60's we used a similar phenomena called a Bologna Bottle.
The "bottle" was a flask with the interior stressed like the Prince Rupert's Drop, but the outside of the flask was tempered glass.
The bottle could be used to drive a nail into wood, but drop in some sand and shake the bottle and it "explodes" like the Rupert!