Continuity mistake: In the scene where Leonard is packing up his collectables to sell, at 15:32 he is dusting what appears to be a Hasbro Marvel Legends Yellow jacket figure, which also has a yellow post-it on the back. At 15:42 he is still dusting a figure but he now holds a different (darker but not yellow) figure from the same series, with no post-it on the back, and the Yellow jacket figure is now on the table (house left of the box of collectables). At 15:56 The Yellow jacket figure has disappeared from the table, and it is not the figure in Leonard's hands either.
New this week Continuity mistake: After Amy returns to the apartment for the Grease DVD and discovers Penny doesn't like the painting, she then exits the apartment with the painting and the Grease DVD with her. When Amy says to Penny she doesn't need her pity, the Grease DVD is placed above the hanging string of the painting. In the next shot, as she walks into the hallway, the Grease DVD is suddenly almost half below the string.
New this week Continuity mistake: In the scene where Howard and Bernadette are about to have sex and Bernadette leaves to "brush her teeth", Howard stretches and lays on the bed uncovered. After Howard's mother yells "over my dead body my son goes to space" and Bernadette appears again and says "I'm ready", then it flashes back to Howard and he is instantly covered up.
New this week Continuity mistake: When Penny is giving Sheldon his haircut, she accidentally shaves the back of his head. The clippers are shown going from the bottom of Sheldon's hair, up to the top of his head. But when Sheldon goes to leave the room, it can be seen only two inches from the back of his head have been shaved off.
New this week Character mistake: After Sheldon has told Barry about the rules of Rock/Paper/Scissors/Lizard/Spock for the first time, Barry then replies "I'm sorry, can you repeat that." When he says "repeat", he correctly pronounces the "r." However, it has already been established throughout the series that Barry has a lisp and anytime he says a word with an "R" in it would always sound like a "W."
New this month Continuity mistake: Right at the start of the episode, Leonard kisses Penny. When he starts kissing her his head is tilted to the right (opposite side to the wall with the camera). When they move to the camera image, his head is tilted to the left (on the side with the camera), and when they move back his head is back tilting to the right again.
New this month Continuity mistake: Near the end of the episode, in the canteen scene, Howard shows the card trick to Sheldon again. The card at the bottom of the deck is the 2 of hearts as he takes them from the box. Sheldon then takes this card from near the top of the deck when Howard puts them on the table. The deck is not shuffled between times.
Other mistake: While the group are trying to figure out how to play Halo without Howard, Leonard jokingly suggests cutting Raj in half. Raj responds, "Oh sure, cut the foreigner in half. There's a billion more where he came from." But Penny is in the room with them, so there's no way he should be able to talk in front of her, or even if he's been drinking, the fact alcohol helps him isn't realised until the next episode, so the fact he can speak with her there should have surprised everyone, including him.
Factual error: Sheldon says the movie Gremlins "baffles" him in regards to the instructions being very clear."Don't feed the gremlins after midnight. Don't get the gremlins wet." However, these instructions are only for caring of a Mogwai, not gremlins (and the gremlins are formed by Mogwais eating after midnight). Sheldon, of all characters, would not mistake Mogwais for Gremlins and he would know the exact wording of the instructions.
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.
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.
Factual error: During the final scene of this episode, Sheldon steps out of his office wearing a gas mask and engages Leonard in conversation where he then states he is making hydrogen sulphide gas (more commonly known as H2S). Leonard correctly identifies this as highly flammable. However, this gas is far more dangerous and is harmful to the human body at as low a concentration as 20 parts per million (ppm), can cause permanent damage at 100ppm and is fatal after two breaths at 500ppm. So for Raj (and his bird) to be completely unharmed in a high concentration of H2S (noted by the fire) is impossible.
Factual error: Sheldon's voice becomes squeaky when helium is pumped into his office. But if the room contained enough helium to make his voice squeaky just by breathing, Sheldon would actually be suffocating due to lack of oxygen, the lighter helium having displaced the heavier oxygen. You can do it with a balloon because you can breathe normal air between huffs, but if you're in a room full of helium, you won't last long before passing out and asphyxiating.