The Burning - S9-E16
Continuity mistake: At the beginning of the episode, when Puddy is farewelling Elaine on the street, he is standing on the sidewalk and leaning through the driver's window. The following shot when she pulls out quickly, you can see through the windows of the car that Puddy is nowhere to be seen.
The Slicer - S9-E7
Continuity mistake: When Elaine is woken up by her neighbor's alarm she looks at her own bedside alarm clock and it shows 3.30 AM. In the next shot when she buries her face in her pillow and screams, that clock shows 3.29 AM. (00:00:50)
Continuity mistake: When Newman and the landlord look into Kramer's apartment through his peephole, the background doesn't match from when they look in and when he opens the door.
Factual error: George asks for a nickel from Jerry for his candy bar. He then proceeds to put only 3 coins into the machine for a $0.50 candy bar. No 2 coins would require a nickel to make 50 cents.
Continuity mistake: The private jet that The Limo pulls up to on the ground and the one that they show the gang on while flying are two different types of planes.
Factual error: At several points during the case, the prosecutor introduces witnesses by saying "The state calls." Legally, Massachusetts is a Commonwealth, not a state, and that is how it is referred to in court. (See any episode of "Ally McBeal" or "The Practice.") However, even this would be incorrect here, as the episode makes it clear that the "Good Samaritan" law is a local Latham statute, not a Massachusetts law. In this case, "The people call." would be correct.
The Frogger - S9-E18
Factual error: Frogger machines kept scores, but they didn't keep the initials of the person who got the score.
Other mistake: In the scene where Jerry, George, and Elaine are in the coffee shop and Kramer walks in with the dummy mailman with the bucket over his head, Kramer remarks how nobody entered the post office while he was outside protesting. Jerry remarks, "That is because it is Sunday." If that is true, how can the group be gathered at the coffee shop? There is a red sign by the entrance of the coffee shop showing the business hours, and the coffee shop is supposedly closed on Sunday.
Continuity mistake: After his gig, when Seinfeld is talking to Kramer in the backstage, his T-shirt is all wet around the neck and chest, and a couple of seconds later it appears dry.
Continuity mistake: When Elaine and her new boyfriend are eating in the restaurant, her bangs are to the side. The shot goes to a close-up of her boyfriend, in the next shot her bangs are across her forehead. Then in the next close-up of her face, her bangs are back to the side.
Revealing mistake: When Kramer starts rubbing the butter stick over his face, the end of the stick becomes orange from the stage makeup Michael Richards is wearing.
The Cartoon - S9-E13
Continuity mistake: After George and Janet leave The Apartment, Jerry gets mad at Kramer for saying Janet looked like him. He shoves Kramer and the bottom half of the freezer door swings open. The next few shots show Jerry and Kramer from the chest up, but when a wide view shot is shown again, the freezer door is closed. It does not appear Jerry shut the door.
Revealing mistake: When Kramer at the start of the episode puts the hose on the kitchen tap, he jerks the hose as it's not long enough to reach The Fire. If you look at the sink when Kramer does this, it comes easily out of its position on the counter top.
Continuity mistake: When Loretta comes into The Apartment she is carrying a coat and roses in one hand and the other hand is supporting her handbag by her right shoulder (left on screen). In the next shot she is holding the bottom of the flowers with both hands instead of just the left hand.
Continuity mistake: When Kramer and Jerry are talking about the bird being in the hallway, notice how the intercom keeps changing. In some shots the intercom is not set straight and leaning to the right and in other shots it is completely straight. The most notable change is when Kramer is leaving The Apartment. It goes from crooked as he is leaving, then straight while he is outside in the hall and then the entire unit is completely pulled right out after Kramer rushes backs in.
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)
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)
Visible crew/equipment: After Elaine gets out of the taxi, she starts walking on the sidewalk, before chasing after the taxi once it drives away. The reflection of the filming crew can be seen in the windows of the buildings next to her when she starts walking. (00:06:32)
Continuity mistake: When the NBC executives introduce themselves to Bania at the comedy club, their last names have swapped since season 4. Jay introduces them as Jay Chermak and Stu Crespi, when in Season 4, they were Jay Crespi and Stu Chermak.
Continuity mistake: When Elaine is sitting with Puddy in the restaurant when they get back together, the amount of wine in Elaine's wine glass keeps changing.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.