Audio problem: As the doctor is explaining how he thinks there were other factors at play to stave off the infection, when he says "something perhaps..." his mouth/lips do not move.
Audio problem: When it cuts from Elaine to Kramer, the audio of what Kramer says is audibly split, as it sounds like he was speaking previously but it was cut off. (00:11:30)
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.