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: Raj and Sheldon are watching TV in Raj's apartment and we hear music playing. Sheldon asks if the woman on TV was Aishwarya Rai to which Raj says yes and then they argue about her and Madhuri Dixit. The song playing was from the Bollywood movie Kaho Na Pyar Hai, but neither of them are in the movie - the lead actress was Ameesha Patel.
Character mistake: When Sheldon arrives at the apartment with his Nintendo 64 in the box, he tells Leonard that they can play Super Mario 64. He then proceeds to say, upon finding a memory card, that they can pick up where he left off. Super Mario 64 does not make use of the memory card, all of the data is saved on the cartridge.
Continuity mistake: When Sheldon emerges with all of the bath item gift baskets for Penny, he drops them on the floor and chair. Between shots one of the baskets on the chair changes from being an upright green-ribboned basket, to a toppled-over white-ribboned basket.
Factual error: Leslie Winkle takes shelter with Howard in the middle of a paintball game. Her gun has no hopper for paintballs and thus no ammo, so it's useless, despite her apparently using it outside seconds earlier. This isn't a model with an internal magazine - the port to attach the missing hopper is plainly visible.
Other mistake: Sheldon is an obsessive compulsive and picky person and he picks a pre-designated seat in all places. When he enters Penny's apartment to talk to her he promptly sits on the couch, which was not where he chose 'his seat' to be in the last episode of the first season. It seems out of character that he would sit there when he has a ready-chosen spot and that his nature is as it is.
Continuity mistake: In the laundry room when Penny is talking to Sheldon, Sheldon takes some time arranging a blue shirt on his plastic laundry folder. Then it suddenly turns into a pair of socks, which he folds and then picks up the blue shirt again. There was not enough time for him to switch out the shirt for the socks.
Continuity mistake: When Penny is talking to Leonard's mother about her father she says (not exact quote) "My mom could've said 'Bob, get over it, she's a girl, move on'." However, we find out in a later episode that Penny's father is called Wyatt, not Bob.
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.
Continuity mistake: In the opening scene, just after Howard says, 'Creepy good or creepy bad?', there is a shot where Howard is holding his food, even though Leonard hasn't given it to him yet and it isn't there in the shot before or after. After Leonard gives the food to Howard, the exact same shot is used after he says, 'I'm not necessarily talking about the food', so the shot was taken from there and it is shown twice.