xroach(1) is an ScreenToy? for X11 systems which simulates cockroaches that scurry around your desktop and hide under windows. When you move/close/minimise the windows the 'roaches are disturbed and scurrry around until they find another nice hiding place.
Packaged binaries widely available e.g. from http://packages.debian.org/stable/games/xroach or http://www.osxgnu.org/