When Antonio (David Labiosa) the busboy enters Jerry's (Jerry Seinfeld) apartment, the number on Jerry's door is 3A, not the normal 5A.
The overhead shot of Elaine in bed shows her male friend taking the covers. In the side shot, they are both fully covered by the bed covers.
When George and Kramer leave Jerry's apartment to see Antonio, Kramer is wearing a two-tone, buttoned shirt. When they arrive at Antonio's apartment, Kramer is wearing a Harley-Davidson t-shirt under his jacket.
When Jerry says, "I didn't say anything," he is chewing on a bite of spaghetti. In the next shot, his mouth is empty and he is reaching for a piece of bread.
When Elaine is making her speech, she brushes her hair out of her face. When it cuts away to Jerry and George and back to Elaine, her hair is back across her face.
George (Jason Alexander) says that the best public restroom near 65th St & 10th Ave is in Lincoln Center. There is no such intersection as 65th & 10th however, because at 59th St, 10th Ave becomes Amsterdam Ave.
If there had been something as serious as a gas explosion under a New York restaurant that killed five people, Jerry and the others would surely have already heard about it on the news.
When Jerry is on the phone and tells Kramer that the door buzzer is Elaine, Kramer pushes the left intercom button, not the right door-release button, but Elaine still gets in.