MPW’s About Box
The animation shows the imaginary building blocks of a 3 1/2" floppy disc flying together one-by-one from out of a box. When the pieces have finishing compiling an airbrush machine comes and paints the surface of the disc.
It’s a wonderful piece of animation, lovingly put together and hidden in a menu most users would never see. If you weren’t around for the original Mac OS, or just weren’t programing during those days, here’s your chance to see it.
Alas, the YouTube account has been terminated, but there is still a static screenshot.
Update (2014-11-21): @chucker found another copy of the video.