Elaine says she uses the diaphragm as birth control. In The Sponge, the entire episode is based upon her obsession with the sponge.
While George (Jason Alexander) is talking to David Letterman in the hall, Jerry (Jerry Seinfeld) pitches the butler idea to the NBC executives. He changes the idea he & George came up with & pitches it that he gets the butler, not George. George enters the office while everyone is laughing and says to Jerry, "I thought I was getting the butler." George couldn't have known Jerry made the change as he wasn't in the room at the time.