Shakedown is a typical joke to play on your friends, colleagues or family. What it does is suddenly and violently shake your desktop as if it had activated a brutal and aggressive earthquake.
Shakedown is fun to watch all the icons and other desktop elements move about the place, nervously and compulsively while this false earthquake attacks.
To deactivate Shakedown just click on the mouse or press any key on the keyboard, and your desktop will return to normal.