Continuity mistake: When Kramer spills the tomato juice all over Jerry's walls, he grabs a light colored oven mitt to wipe it off. In one shot he wrings out the sopping mitt over the juice pitcher. When the shot changes and he tosses the mitt back onto the counter, the mitt is still the original color with no hint of red stains.
Continuity mistake: Due to the effect of the red glow on Kramer's eyes, he confuses the pitcher of tomato juice from Jerry's refrigerator for a pitcher of milk, pours it into the cereal, then gags and promptly tosses the contents of the bowl into the trash beside the fridge. In the close-up he tries to wipe some of it off the wall, but there's still a huge red mess left on the wall, in the trash, etc. In the next wide shot of Jerry and Kramer, the trash and wall are spotless.
Continuity mistake: When Newman is first eating the chicken in Seinfeld's apartment, the amount of meat on the leg changes without Newman putting down the leg and getting another one out of the box.
Continuity mistake: After crazed Jerry and Elaine leave to get a hat, Kramer picks up the tub of ice cream Jerry had set down and starts to put the lid on. In the next shot, he's not holding the ice cream.
Continuity mistake: In one scene George is solving a Rubik's cube in Jerry's apartment. When he leaves, he places the cube on Jerry's kitchen counter, and it is in the middle of the counter with the red color facing out. In the very next shot, it is moved much closer to the far edge of the counter and the color facing out has changed.
Continuity mistake: After George and Jerry discuss the fact that George will never have sex again, they stand up to leave the coffee shop and George places a large book under his arm. In the very next shot, he is holding the book in both his hands.
Continuity mistake: When Celia breaks out of prison and comes to George's apartment, George opens the door and starts talking with her. After George says "And you decided to pop in" the shot shows Celia but the door has now closed behind her. It would have been impossible to close without us seeing it because Celia would have had to have moved forward to close the door.
Continuity mistake: The exterior of the video store in the episode looks different from the interior. From the inside, we see a neon "open" sign on the window and other writing, and also no exit sign on the door, all of which is contrary to the outside view of the store. (00:09:25)
Continuity mistake: When Morty's exercising first wakes Kramer up, his clock reads 5:30. Then in another shot, the clock reads 5:26. (00:10:05)
Continuity mistake: We find out George's parents sleep in separate beds. His father says "Thirty years ago we came to an agreement. It was the only way I could get some rest. Estelle's got The Jimmy arms." This contradicts S5E10, "The Cigar Store Indian", when George's parents come back from their trip, Estelle finds a condom wrapper in "our bed." Also Frank asks George, "You were having sex on our bed?", and Estelle follows by saying, "Who told you you could have sex in our bed?!" (00:16:50)
Continuity mistake: In the episode "The Suicide", Kramer discusses suicide with Jerry, and says that he'd give someone 72 hours to come out of a coma before all his property is up for grabs. However, in the episode "The Comeback", Kramer tells Jerry that he never knew that people could come out of a coma.
Continuity mistake: Towards the end of the episode, it transitions between the Yankee ball at night and "Susie's" wake which is during the day.
Continuity mistake: When Mike accuses Jerry of murder at Susie's wake, watch the people behind and around Jerry. There are women either side of Peggy, turning around, looking surprised and moving their hands. The next shot, we see Jerry from behind his seat, and everyone has instantly changed to sitting perfectly still, looking ahead with their hands still.
Continuity mistake: In one scene George's desk is placed with room to walk all around. When Steinbrenner walks into George's office, the desk is pressed against the wall and office looks smaller. (00:18:54)
Continuity mistake: In the final scene where Newman is going to eat the bag of muffin stumps, Newman removes the bottles of milk and then takes a bite out of his muffin. He then takes a drink from the glass but he never filled the glass with milk in the first place.
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 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 George enters The Cafe near the start, he takes Jerry's plate and begins eating the fries. After finishing the first fry, his hands are on the plate. Jerry then asks him what happened, and suddenly he has a fry in his hands which are also now raised slightly.
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.
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.