Goof (revealing mistake): The door to Penny's apartment on the fourth floor is directly above the building's street entrance on the ground floor. This would mean that her apartment, and the ones above and below hers, are floating out above the street.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Sheldon states that he has an eidetic memory and that he "never forgets anything", however, he is frequently seen to forget things in various episodes (his door keys, titles of Spiderman comics, actresses who have played Catwoman etc).
Goof (errors made by characters, possibly deliberate errors by the filmmakers): In one of the episodes when Sheldon moves in with Raj, Raj is watching an Indian movie. The actress of that movie is referred to as 'Aishvarya Rai', but it's actually 'Amisha Patel'.
Goof (factual errors): The opening titles are based on a time line of human history. A picture of Abraham Lincoln is followed by a picture of George Washington.
Goof (factual errors): When bringing Penny's furniture up to her apartment, Leonard and Sheldon lay the box on the stairs and Leonard states "Now we've got an inclined plane. Force required to lift is reduced by the sine of the angle of the stairs..." This is incorrect, as the force required to lift it stays the same. The force required to push the box up the stairs is half of that required to lift it.
Goof (continuity error): After Penny finds out they were in her apartment during the night, while Sheldon talks to her she has first her left arm on her waist, then after the cut she has both arms on her waists.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): When putting Penny's furniture together Howard complains over IKEA's pictographic representation-assemble manual and states that this is why Sweden don't have a space program. On the contrary Sweden have a highly developed space program and their base Esrange may be used for launching space tourism, starting in 2011.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): When Howard compliments Penny's appearance in what he refers to as "flawless Russian" he grossly mispronounces the Russian word for "girl," putting the stress on the second syllable instead of the first.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Both Penny and Sheldon mention Superman "swooping down" to save Lois Lane in the 1978 Superman film, when in fact, he actually flew upwards to save her.
Goof (continuity error): In between takes the french toast Penny is holding changes; from being mostly covered with egg to fully covered.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Sheldon suggests that pushing Penny's furniture up the stairs slowly or rapidly makes no difference, because the amount of work involved would be the same. Although the latter is true, as a physicist he would have known that the power input needed (work/time) would be different. A human being can only generate a certain amount of power, therefore pushing the furniture slowly is easier than pushing it fast.
Goof (factual errors): When Leonard, Sheldon, Raj, and Howard are playing their game in the beginning, they reference the word Azeroth which is the name of the world essentially in the Warcraft series, implying that they are playing World of Warcraft. World of Warcraft actually does not have a "Sword of Azeroth" nor are any of the typical key bindings used with the Alt button, rather, spells and abilities are used by numberings on a player's keypad.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): When Penny and Sheldon are driving to the supermarket, Sheldon does not object to Penny's check-engine-light being on (although this fact is not specifically mentioned, we later find out (in "The Maternal Congruence") that the check-engine-light has been on ever since Penny bought her car, so before Sheldon first drove in it.)
Goof (revealing mistake): The laugh track is cut off as the scene changes from when Howard walks in with his "date" to the rest of the group by the buffet table.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): In the store, Sheldon tells Penny that tomatoes are actually fruit, not vegetables. Tomatoes are fruit in botanical terms, but they are vegetables in culinary terms. Though there are culinary fruit and vegetables, botanically, there are no vegetables. A lot of vegetables are botanical fruit.
Goof (audio/visual unsynchronized): After Dr. Gablehauser gestures to the chair and says, "Please," his mouth keeps moving but no words come out. (He probably originally said, "Please sit down.")
Goof (factual errors): When Sheldon is driving with Penny in the car and says assume the weight of the car as 4000 pounds, his weight as 140 and Penny's as 120, he comes up with the total weight as 4400. It should be 4260 pounds.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Leslie tells Leonard that when he looked at Penny his pupils dilated and unless he was a heroin addict that is a sign of sexual attraction. Heroin addicts do not have dilated pupils. Opiate users, including heroin addicts, have pinpoint pupils. Even though Leslie is not a Pharmacist, Pharmacologist or Physician, she should know this.
Goof (revealing mistake): The morning after Leonard and Leslie have sex, Leonard picks up his glasses, putting his finger through the place where the lens should be.
Goof (audio/visual unsynchronized): Leslie's fingering of the violin is clearly off compared to the music.
Goof (continuity error): In a scene at the cheese cake factory where Sheldon is explaining why the single decker burger is better than the double decker burger from Big Boy, you can see him taking a bite and the burger is almost all gone and then it switches to a different angle as Leonard is speaking and suddenly his burger is much larger again.
Goof (incorrectly regarded as a mistake): Leslie tells Leonard to wear protective goggles. It's not generally accepted that if you're wearing glasses, they're enough to provide protection. However, the only glasses accepted are safety glasses. Protective goggles will cover regular glasses, which is the reason they are so large and have grooves where eyeglass handles pass through.
Goof (incorrectly regarded as a mistake): When Sheldon wakes up in the morning after Leslie stays the night, his head is on the end of the couch nearest to the door. This is in direct contradiction to what he tells Penny in the future about how the headboard is oriented away from the door to serve the ancient imperative of protecting oneself against marauders. However, given that in the previous scene he is sat not knowing what to do, it can be assumed that he sat there until eventually falling asleep out of exhaustion, without having planned it out, as evidenced by him still being sat in 'his spot'. Alternatively he may have learned of the ancient custom between this and the future episode.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Homo Habilis is properly pronounced with the stress on "hab" instead of on "bil" as done by Leonard and Sheldon. Ironically, though Leonard was insulting Kurt by refering to him as H. Habilis, Leonard is actually closer to the average height of H. Habilis which was 4'3".
Goof (crew or equipment visible): When the guys attend Penny's Party, there is a guy with a hard hat on. Studio Lights and several other pieces of studio equipment are reflected in his hard hat.
Goof (continuity error): The morning after the original Halo Night, Sheldon says he is following the routine he has followed every Saturday morning since he and Leonard moved into the flat. Hence suggesting that Halo Night is on a Friday. However, later in the episode, when they ask Penny to take part in Halo Night and she says for her it's dancing night, he asks her if she dances every Wednesday night. Yet the suggestion is that Halo Night is a fixed night of the week.
Goof (continuity error): Raj speaks in front of Penny (which he usually cannot do) without being intoxicated in the beginning, after they re-enter the apartment.
Goof (factual errors): The sounds heard and actions described by Penny ("I just blew off your head!") do not match Halo's game play.
Goof (continuity error): While making up the couch, and arguing with Sheldon about it, the string on Penny's sweater changes position. She hits it with her hand accidentally resulting in it ending up in her cleavage, it is still there when she turns around. The camera switches to a wide view and you can see that she doesn't move her arms anywhere near it but in the next close up shot it is hanging down again.
Goof (errors made by characters, possibly deliberate errors by the filmmakers): Sheldon is a mysophobe, so he would not have taken the packed chicken he threw in the garbage bin for consumption later.