In the 1990s I worked at an investment bank, all the developers had X terminals (these were workstations that just ran X servers, they did not have any other local compute or storage resources). I discovered one day that I could run a program and direct the display to any X terminal in the network. There were some screensaver-type programs that would make everything on your screen a mirror image, or appear to melt down and run off the bottom of the screen. It made for some fun pranks.