Jerry (Jerry Seinfeld) doesn't have cable in this episode - all he has is over-the-air channels with poor reception. In the previous episode, The Deal (1991), he had cable with all the channels including "The Naked Channel".
When Kramer is trying to convince Jerry to get the cable hookup, the top of the set wall, where the ceiling of Jerry's apartment should be, is visible.
When Kramer enters Jerry's apartment during the baby shower and Elaine asks him who this guy is, the camera cuts to another angle and you see Kramer in the background talking, but the audio is of Elaine speaking, not Kramer.