This project will self destruct in 10 seconds (approx.) (Download) 
WHAT TO DO: Download, press the green flag, wait ten seconds (show by the timer), and then it will close.
HOW IT WORKS: The script multiplies a variable by itself so many times that it crashes scratch and causes it to close.
Ad + bigger explanation: http://scratch.mit.edu/forums/viewtopic.php?id=55749