Easter egg: On Disc 4, go to the Episodes list. Select to the last episode: "The Finale". If you go down at the bottom there is a round object that is lighted up. Click on it, and then it shows you an alternative ending of the last episode of Seinfeld.
Easter egg: On the first disk of volume 1, season 1, if you go to the extras menu, press up until the jalapeno pepper on the fridge in the top of the screen is highlighted. Press it, and you'll see a short camera test of various sets with Jerry Seinfeld and Jason Alexander, with commentary by director Tom Cherones and Production Designer Tom Lazari.
Answer: Composer Jonathan Wolff used a synthesizer, although in seasons 7-9, a real bass is used in addition. Wolff also recorded himself making hundreds of mouth noises, pops, and slaps to add to the synthesized bass licks so that each episode has a different theme. The only real "back-story" is Jerry Seinfeld was having trouble coming up with a theme song and talked to a friend who happened to know Wolff. They wanted to avoid that cheesy late 80's sit-com theme song and Wolff came up with what we enjoy now. Jonathan Wolff has also talked about this further in interviews, recently Reed Dunela interviewed him, so for a fuller account of his story; check out "The Wolff of 116th street".
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