Continuity mistake: When George is lying on the floor in his underwear, a newspaper is on his right side. When they take the reverse shot (Jerry's view of him lying there), the newspaper is on George's left side.
Visible crew/equipment: After Jerry, Elaine, George and Kramer walk out of the orange stairwell, there is a shot as they come out the door. A car drives past. The crew is reflected in the window.
The Red Dot - S3-E12
Continuity mistake: After Elaine unwraps her cashmere sweater, Kramer wraps the ribbon around his neck in a scarf-like way and then lies back on The Couch. In a long shot of The Apartment (as Elaine exits the bathroom), the ribbon is gone, but when it cuts to Kramer and he asks about The Red Dot (and for the rest of the scene), the ribbon is back.
Continuity mistake: At The Airport, while deciding to take The Limo, Jerry's scarf moves on and off his shoulder between shots.
The Letter - S3-E21
Continuity mistake: While George is talking to Nina about the painting, Jerry can be seen taking a bottle of water from the refrigerator. He's then seen holding the bottle when buzzing up Elaine, but then when talking to Nina about the "pop-in", the bottle's gone. It's then back in the next shot when Nina says she's leaving. (00:15:13 - 00:16:00)
Continuity mistake: One shot shows George beginning to step out of the car, with his leg out of the vehicle, but in the next shot, he appears to be fully inside the car. (00:06:30)
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".
Bishop73