After Kramer makes his first entrance into Jerry's apartment, he closes the door behind him. While he's telling Jerry about snubbing Gail, Jerry gets up and goes to the kitchen. The door is now open. Later, when Kramer enters the apartment again, he pushes the door almost closed. While he's telling Jerry about kissing Gail, the door changes positions several times.
George (Jason Alexander) threw Jerry (Jerry Seinfeld) a script while telling Elaine (Julia Louis-Dreyfus) about his therapist, and as Jerry flicks through it, we can see it's blank.
George (Jason Alexander) said that he and Jerry (Jerry Seinfeld) pitched "the butler story" to Russell Dalrymple (President of NBC), but this was false. In episode 4.10, The Virgin (1992), we saw they pitched it to Rita Kirsen.