If you catch General Motors' commercials, you may notice a quick, flashing sequence just before the GM logo sequence. This can be viewed by frame-stepping.

The first two frames have a stage background with the words "GM's One Second Theater" or something very similar, with a subtitle. The next frames display pictures with humorous information about the commercial.

The egg is actually less than one second, and in fact I've viewed the commercials several times before I noticed this. The only two eggs I've seen so far were in the dancing elephant and the railroad commercials, but I'm sure there will be more.