The clock does change since the desktop background isn't over the menubar...
My favorite on the older Classic Macs (OS 9, 8, etc) was to put an AppleScript in the Startup Items folder that told the computer to shut down, and an item in the Shutdown Items folder that told the computer to restart. The end result was an endless loop of startup/shutdown. The only way to get rid of it was to startup with extensions disabled, which didn't launch anything in the first folder. The result was always hilarious.
A modern version of this would be to make an executable reboot command and set it as a login item.