Other mistake: When Jerry, George and Elaine go out to Long Island to the party, George sees his lady co worker friend who says "guess what property I just sold...129 West 81st". That is Jerry's own address, which wasn't sold to anyone.
Revealing mistake: When Kramer and his lawyer, Jackie, are in the taxi; when Jackie says "who told you to have a pow wow", a man is seen walking across the rear window. The taxi is supposed to be moving, but the man's position stays the same (the taxi should be pulling away from him). The actual traffic filmed for the green screen doesn't seem to react to a man jaywalking in front of them either, as it was someone walking across the set.
The Gymnast - S6-E6
Continuity mistake: When George is at his girlfriend's mother's house, the plates on the table switch around. Then the order he stacks them changes. When he picks them up, the plate with the chicken is in the middle with a plate with a napkin on top, then in the kitchen, the plate with the chicken is on top.
The Calzone - S7-E20
Visible crew/equipment: In the scene where Elaine questions her boyfriend in front of her apartment, look carefully at the end of the conversation. When her boyfriend turns and walks away, you can see where the green screen ends, with the crew members/cameras standing on the set. (00:09:25)
The Slicer - S9-E7
Continuity mistake: At the end of the episode, after George has successfully airbrushed himself out of Kruger's picture and reinserted an authentic picture of Kruger, Kruger picks up the picture and explains to George why he doesn't think the mole Kramer discovered in Kruger's cancer screening is anything to worry about. After George says "Whatever" and just before Kruger begins explaining the story behind the picture to George, he tilts the picture towards the camera and if you look closely you can see that George is still in the picture. (00:11:00 - 00:22:20)
Continuity mistake: Jerry and George are at the pharmacy. As George pays the bill and is heading out, behind Jerry there's an old lady at the counter. The camera changes and the same lady disappears and you can see her in other side of the store heading again to the counter. (00:02:25)
Continuity mistake: In the first scene (approximately 3 minutes in) where Jerry points out the red-headed woman in The Parking Garage to George, she is leaving her vehicle in a section of the garage that is labeled 14 with a green background. However, later (approximately 23 minutes in) she is shown returning to her car in section 14, but the color is now yellow.
Continuity mistake: The inside and the outside of the Costanzas' home do not match up. From the inside, you can see that if you walk in the front door the kitchen would be on your left and a sitting room-type area is on your right (accessible from the living room). However, from the outside, it shows bay windows on what would be the left (kitchen) side and a door to another townhouse on the right (sitting room) side.
The Statue - S2-E6
Continuity mistake: Near the end of the episode, Kramer acts like a cop to get back The Statue. The door is almost completely closed. Just before he leaves, the door is suddenly open about one foot, even though it hasn't been touched yet.
The Strike - S9-E10
Visible crew/equipment: When Jerry is chasing after Gwen and when he returns to the table, you can see the shadow of the boom mic on the wall. It is most noticeable to the right of the framed picture. (00:20:57)
Continuity mistake: At the beginning of the episode, the bag on the counter keeps moving and disappearing, and reappearing.
Continuity mistake: Donna's purse strap changes position on The Couch throughout the scene, when she's there when George brings up her liking the commercial.
Character mistake: George makes a big deal about wanting to say "I love you" to the girl he's dating and says he's never said it to a girl, just a dog once, and he wants to say it just once. But in s02e01, "The Ex-Girlfriend", George tells Jerry he had to say "I love you" to Marlene when she told him she loves him.
The Suicide - S3-E15
Continuity mistake: When George and Elaine are at the psychic, Elaine is saying she doesn't know how the psychic can put a cigarette in her mouth. At this point the psychic has the cigarette in her mouth and her hands are clasped. In the next shot, the cigarette is now in her hand.
Continuity mistake: When George goes into the suit shop after being told about the sale, he sees another man trying on the suit. George tells the man the sale is on Monday and the man takes off the suit coat and George is holding it in his hands when the saleswoman says the sale is on Friday. In the next shot, she has the coat and is hanging it despite never taking it from George.
The Implant - S4-E19
Continuity mistake: After George puts a couple of the snacks in his mouth, he takes a bite of the next one before Father Jessup says George is great comfort. In the next shot, the snack George is whole and no longer has a bite taken out of it.
Continuity mistake: When Jerry opens the magazine to the article about him before handing it to George, the left side is mostly black with a picture and the right side is half black with "now" in big yellow letters. In the next shot of him handing the magazine to George, the page seen is mostly white with fine print and a small picture. In the next shots of George reading it, the magazine is back to where Jerry had opened it up to the first time.
The Glasses - S5-E3
Continuity mistake: When George bites into the onion, you can see the top of the onion is facing up or towards the camera, next to his finger. In the next shot, you can tell the onion has rotated position. You can see the root is to the side, so the top would be on the side instead of up.
Answer: The name is Delores. He shouts that name at the end of the episode. Then in a later episode, "The Foundation", he runs into her. And he repeatedly calls her Delores.