The three things Elaine & George mumble under their breath that Jerry can't hear & aren't audible are: 1) When George and Elaine are sitting on Jerry's couch, Jerry asks Elaine if she saw him try to give Kramer the keys back, she says, 'I mean, it was complete bullshit but I saw it.' 2) When George is letting Jerry into Elaine's apartment, Jerry is going over the long explanation on how he should be the one with Elaine's keys anyway, George replies, "You're right how did I miss that? Maybe because it's a crock of shit." 3) At the end of the episode, Jerry & Elaine are talking about her wanting to be a writer. Jerry is explaining 'show business' and what she has to do to be able write a sitcom. After getting annoyed and asking to just be able to watch the show she whispers, "Oh, God, what an asshole."
During filming of "The Keys," Julia Louis-Dreyfus was pregnant with her first child, Henry. Throughout the episode, she hides behind various props to hide her pregnancy as her character, Elaine, was not pregnant.
The music Kramer's (Michael Richards) mother is listening to in the background when Jerry (Jerry Seinfeld) calls her is "Vesti la giubba" ("Put on the clown suit") from "Pagliacci."
The hippies that give Kramer a ride part of the way to L.A. are based on the Manson Family, four of whom were convicted along with Charles Manson of the 1969 Tate/LaBianca murders.
After Candice Bergen and the set of Murphy Brown (1988) made a guest appearance in this episode - in which Kramer (Michael Richards) is hired as an actor to play Murphy's secretary - Jerry Seinfeld and Larry David returned the favor by appearing as themselves on Murphy Brown creator Diane English's other sitcom Love & War (1992), episode Let's Not Call It Love (1993), where they receive a Seinfeld script written by a Blue Shamrock customer, in which Kramer sleeps with Elaine (Julia Louis-Dreyfus). This also echoes Elaine's writing a Murphy Brown script in this episode.