Reminds me of my university days...
When someone walked away for an extended period without locking their terminal, one of us would sneak over and do a quick 'xhost +' and then wait for them to come back.
Once they sit down and start working again, we would run 2 dozen copies of neko on their terminal, resulting in a mass of little animated kittens chasing their mouse cursor.
Ah, the lost days of innocent fun.
We'd run `xset s 1` so that the screen saver would kick in after one second of inactivity.