New this week Continuity mistake: The Stevenson Award in Sheldon's office reads "Sheldon Cooper, PhD." But, in the "Dennis Kim" episode we are told Sheldon was 14.5 years old when he earned that award - 1.5 years before earning his PhD at age 16, so the award should not show the title of PhD.
New this month Continuity mistake: When Leonard is standing outside the apartment his hair is tucked under the band of the wireless cam he has on his head, but when he is crawling on his hands and knees through the apartment his hair is out from under the band and is hanging in front of his face.
New this month Continuity mistake: When Sheldon sneaks into Leonard's bedroom while Leonard and Penny are sleeping, Penny has her arms out over the blanket and Leonard has his on his pillow in front of his face. When Sheldon leans over Penny only her hands are on top of the covers and Leonard's are tucked under his pillow.
New this month Other mistake: Five minutes into the show, Sheldon has written down what a dice roll will tell him what to do. He rolls the dice, pauses and looks at the list to see what he has to do for that dice roll. The problem is he has an Eidetic memory and wouldn't take the time to look at the list when he can already see it in his head.
New this month Revealing mistake: Throughout the series much is made of the fact that Howard's mother is grossly obese, and in The Engagement Reaction (S4 E23) it is even mentioned that her arms are hugely oversized. However, at the end of this episode we see her arms when she grabs Raj to stop him climbing out of the window, and they are the arms of a perfectly normal woman - they aren't overweight at all.
Factual error: There is not a snowball's chance of Howard becoming an astronaut. He suffers from Intermittent Cardiac Arrhythmia, something about which he is completely open. This is easily detectable by a simple electrocardiogram, which is a fundamental part of the many medical examinations a potential astronaut will have to pass. He wouldn't even be allowed to start basic training.
Factual error: At the very beginning of the episode Leonard says "So you see what you're eating is not technically yogurt because it doesn't have enough live active acidophilus cultures." He is implying this is a scientific fact (he's not just giving his opinion on yogurt.) But to meet the U.S. standards for yogurt, only the starter cultures Lactobacillus bulgaricus and Streptococcus thermophilus are required, not Lactobacillus acidophilus. The presence or absence of L. acidophilus does NOT determine a food's identity as yogurt (which Leonard's line is implying).
Factual error: Penny picks up a hand gun, pulls back the slide to ensure the chamber is empty and then loads a magazine into the butt of the weapon and hands it to Leonard. He starts to smooch her and shoots himself in the foot. Problem is, Penny would have had to work the slide again to get a bullet from the magazine into the chamber for this to happen. She pulled the slide far enough back that if there had been a bullet in the chamber already it would have ejected.
Continuity mistake: At the end when Sheldon has got a burger, the amount of burger left changes depending on the camera angle. Most noticeable when he asks Penny about permanently reserving the table - between shots the lettuce disappears, the bun changes colour, and the bite marks change.
Character mistake: Being the first to play in the "time machine," Leonard says he will set the date for March 10,1876. Howard says "Good choice. Alexander Graham Bell invents the telephone and calls out for Doctor Watson." Bell's assistant, Thomas A. Watson, was an experienced electrical designer and mechanic, but he did not hold an advanced degree. It is well documented that the first words transmitted over the telephone identified him as Mister Watson.