The Sun 3/50's pixel buffer was world readable and writable by default, and in console mode had an area at the bottom not affected by scrolling. One could invert random horizontal bars across the screen, transpose the bitmap, or apply a sine wave to persuade the user the massive TV set on top of their workstation was broken. Or, fade text in and out as if the machine was commenting on the user's ineptitude. Much fun was had by all.