Munching Squares

 MUNCHING SQUARES n. A display hack dating back to the PDP-1, which
       employs a trivial computation (involving XOR'ing of x-y display
       coordinates - see HAKMEM items 146-148) to produce an impressive
       display of moving, growing, and shrinking squares. The hack usually
       has a parameter (usually taken from toggle switches) which when
       well-chosen can produce amazing effects. Some of these, discovered
       recently on the LISP machine, have been christened MUNCHING TRIANGLES,
       MUNCHING W'S, and MUNCHING MAZES.