Wasn't that running in its own window [1]? However I'm pretty sure that somebody made it render directly on the screen below all the other windows, or in front of them. I remember cockroaches scrambling to hide below windows [2] or snow accumulating above windows titles [3].

[1] https://cyber.dabamos.de/unix/x11/#xeyes

[2] https://cyber.dabamos.de/unix/x11/#xroach

[3] https://cyber.dabamos.de/unix/x11/#xsnow