The Luminous Fish Effect - S1-E4
Continuity mistake: When Leonard and Sheldon are walking downstairs, Sheldon stops and pins back up the caution tape that is in front of the elevator. Between shots, the other strip of caution tape untwists itself. (00:01:25)
Audio problem: When Sheldon is knocking on Leonard's door at the start, the sound is out of sync with the action.
Factual error: Sheldon has a rigid schedule. Halo Night is known to be on Wednesday night. Penny sleeps on the couch in Sheldon and Leonard's apartment. The following morning, Sheldon cannot watch Doctor Who on BBC America because Penny is sleeping on his spot on the couch. He states that he has been watching Doctor Who every Saturday at 6:15 a.m. The following morning should be Thursday.
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Penny is having a go at Sheldon and Leonard, there is a shot of some metal pans with stage lights visible in them. (00:12:30)
The Jerusalem Duality - S1-E12
Visible crew/equipment: When Dr. Gablehouser is giving his speech about Dennis joining them, stage lights are reflected in his glasses and his wine glass. (00:16:30)
The Cooper-Hofstadter Polarization - S1-E9
Revealing mistake: When Leonard and Sheldon are fighting near the end they bump into the wall, which visibly shakes. (00:15:40)
The Fuzzy Boots Corollary - S1-E3
Revealing mistake: When everybody is on their laptops at the beginning of the episode, you can clearly see in many shots that their screens are black. (00:01:20)
The Middle Earth Paradigm - S1-E6
Visible crew/equipment: When Sheldon is being asked not to embarrass Leonard, the stage lights can be seen in the pans behind him. (00:05:10)
The Luminous Fish Effect - S1-E4
Continuity mistake: When Sheldon's mom is saying the prayer, the bread roll that Raj is holding swaps hands, and then it disappears in the shot where she tells them they don't have to join in with the end of the prayer.
The Big Bran Hypothesis - S1-E2
Visible crew/equipment: When Sheldon is mentioning about the coffee table having a garage sale, there is a shot of Leonard with all the stagelights reflected in the kettle. (00:06:40)
The Hamburger Postulate - S1-E5
Audio problem: When Leonard and Leslie continue to practise together after the other two musicians have left (Leslie now being the only violinist), vibrato from a violin can be heard - from observing Leslie's left hand she is not applying it.
Continuity mistake: In the electronics store, when the man asks Sheldon which hard drive he should buy in the first shot he is holding the green box in his left hand. Next shot it is under his arm. (00:12:50)
The Hamburger Postulate - S1-E5
Character mistake: When Sheldon knocks on Penny's door to seek advice about the tie on Leonard's doorknob, he does not use his typical triple knock. (00:07:43)
First time he knocks 3 times is in Episode 2 of Season 1. First time knocking 3 times followed by saying the name is episode 10 of Season 1. The ritual of 3 knocks and 3 times saying the name and then stopping is Episode 5 of season 2.
Sheldon knocks three times because he once walked into his parents bedroom and saw his father with another woman. He's been doing the triple knock since he was a teenager.
Yet, he didn't in the show till Season 2. Funny ain't it?
Suggested correction: A one-time lapse in someone's usual behavior does not count as a "character mistake", even in the case of someone given to ritualistic behavior as Sheldon is.
Ah, but in an episode he explains he had developed this particular ritual at age 13 after walking into his parent's bedroom without knocking and seeing his father having sex with another woman. He says he started knocking 3 times since then and would never forget. So its not consistent and a mistake as this is not the only example one can name.
The Bat Jar Conjecture - S1-E13
Continuity mistake: At the end, when Leonard is gloating over beating Sheldon, his position on the sofa keeps changing in relation to the arm. (00:18:50)
Character mistake: Wolowitz warns his fellow halo players that their enemy is "charging his Plasma Rifle". This is impossible since only the plasma gun can be charged up. (00:20:00)
The Grasshopper Experiment - S1-E8
Continuity mistake: When Raj's parents tell him to put his laptop down and gather his friends, they all huddle around the one-seat sofa. Sheldon is crouched to the left of the seat with his hands on the sidearm, yet in shots angled at the left he has disappeared from his place (as to not obstruct these particular angled shots.) (00:02:00)
Continuity mistake: When Penny is telling Howard and Raj about Sheldon's "drug addicted cousin" her scarf keeps jumping in and out of her jacket.
