Continuity mistake: Jerry is smothering George with the pillow when Elaine walks in. First shot and a black nurse is walking behind her. Cut for one second to Jerry, back Elaine and the same guy is still walking, exactly where the view cut the first time. (00:06:25)
Continuity mistake: At the beginning of the episode Jerry tells Elaine that he vaguely remembers "doing something"; Julia Louis-Dreyfus puts the remote down and brings her hand up twice in two separate shots. (00:01:30)
Continuity mistake: Elaine walks up to George in bed, and she asks him if anyone's got his apartment yet. For the brief part of dialogue about the zen lifestyle thing, the top sheet is rolled up in a noticeably different way from the rest of the scene. (00:07:00)
Continuity mistake: On his deathbed George triumphantly utters "There's nothing wrong with me!"; the doctor cools his enthusiasm down though, saying that he wouldn't go that far. His hands are crossed in front of his body - at the cut though he's suddenly already browsing through George's medical file. (00:08:10)
Continuity mistake: The doctor is examining George. George yells into the stethoscope so he takes the buds off his ears. Not just that; he removes the instrument and puts it around his neck. George then freaks out and starts naming various odd and even rather harmless conditions; the doc is wearing the stethoscope again. Flirting with Elaine you can see the instrument sorta shuffles around, with part of it exposed and part of it under the scrubs' collar, now the left side, now the right side. When Jerry breaks off their idyll with the Romeo and Juliet reference, the stethoscope is back around his neck, only to be again in use when George asks "With a knife?" (00:08:00)
The Statue - S2-E6
Continuity mistake: The first time we see Ray, he kisses his fiancée's hand. Elaine in that shot is holding her papers, with the thicker black book closest to her chest. A couple of shots later when he bows to "Jerry, lord of the manor" the books in Elaine's arms have switched position. (00:05:50)
The Statue - S2-E6
Continuity mistake: George had enough of Ray's pawn shop story and jumps up calling him a thief. Watch the couple at the table; the woman, wearing a purple sweater, has her hand on the man's arm in the reaction shot, when nothing of the sort was happening in the wider angle. (00:15:30)
The Statue - S2-E6
Continuity mistake: During the scene at Monk's, Jerry bumps George on purpose making him spill some coffee. George is holding his cup in the right hand and the menu with the left. In the reverse shot you can see Jason Alexander put the cup down, held in his left hand. (00:14:20)
The Jacket - S2-E3
Continuity mistake: When Elaine's dad says "Pipe down, chorus boy" to George, suddenly a hotel staffer in red appears in the recess by the lamp. In another blatant continuity mistake, in the shot that follows George is suddenly without glasses. (00:17:50)
The Jacket - S2-E3
Continuity mistake: Elaine's intimidating father gets up and tells Jerry and George in his gravely voice "I'm going to the bathroom." The newspaper on the table changes spot before and after said shot. (00:15:30)
The Jacket - S2-E3
Continuity mistake: At the end of their strategic break in the men's room, George tosses his paper towel in the bin to the right; however the previous shot ended with Jason Alexander turning around having the towel in his left hand and glancing towards the basket on the left. (00:13:55)
The Jacket - S2-E3
Continuity mistake: In the reaction shot with Alton Benes scoffing at George and Jerry's sissy choice of drinks, a woman with a coat in hand is walking behind him, towards the door. In the next shot, no trace of the woman, just someone in a bicolor puffer. (00:10:25)
Continuity mistake: Jerry and Kramer are arguing about the bet when Kramer is having a glass of milk. The phone rings cutting them off, and Kramer's glass suddenly from his mouth goes to his hip. (00:10:25)
Continuity mistake: George drinks from the bottle of anti-acid medicine, puts the lid back on, then at the "Yes, she wants me to like her" bit the lid is off again. (00:08:40)
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.