On the End Credits screen, entering one of the following four codes without the quotation marks, "BOIDUTS", "YNNIF", "SKCUS", or "NAMTAH", will trigger one of four short videos:

The first video is a montage of video footage recorded at Viacom New Media featuring the developers playing around during development (including running around outside during a thunderstorm), showing off a production baby, and ending on Butt-Head saying "Dumbass!" while the word is superimposed over a picture of a developer.

The second video is another montage of videos and pictures recorded during development (including the team going swimming and posing on a couch with Beavis and Butt-Head statues) set to an original rock song written for guitar and sung by one of the developers. Hatman also makes appearances in this video.

The third video is a montage of video footage recorded during the making of the game's beta, which according to the video was completed on August 25, 1995 at 4:45 in the morning. The video prominently features the developers excitedly screaming "Beta" over and over again, before showing them lying in the hallway of the studio exhausted and ending with the quote "These kids are intense...." on screen.

The fourth video is a crudely-made CG animation of Hatman floating through space, and is believed to be the earliest instance of the easter egg made for a game.
Contributed by MehDeletingLater