The Financial Permeability - S2-E14
Continuity mistake: Sheldon opens the can with money in and puts the lid on the side, However in some shots he has the lid in his hand. (00:04:00)
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The Financial Permeability - S2-E14
Continuity mistake: When Sheldon is holding the money out to Penny, the can that is being held by Sheldon is constantly moving up and down in height in relation to his shirt. (00:04:00)
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The Financial Permeability - S2-E14
Continuity mistake: When Sheldon asks Penny if he lent her enough money, the container he is holding opens on its own. (00:09:25)
The Maternal Capacitance - S2-E15
Continuity mistake: After Leonard's mother says, 'Tell me about it', her head was tilted downwards, but in the next shot, she was looking straight again. (00:04:35)
The Cushion Saturation - S2-E16
Continuity mistake: When Howard and Leslie are in the paintball shed, Howard's paintball ammo pack is closed, but when he and Leslie start kissing, it's open.
The Work Song Nanocluster - S2-E18
Continuity mistake: When Penny puts the box down at the start it is closed. Camera cuts and it's open instantly.
The Work Song Nanocluster - S2-E18
Continuity mistake: When Penny gets the package, the position of the box on the counter keeps changing position.
The Dead Hooker Juxtaposition - S2-E19
Continuity mistake: In the scene after the boys have followed the new neighbor out and Sheldon and Penny are left eating alone, the utensils Penny holds change from chopsticks to a plastic fork and back several times.
The Dead Hooker Juxtaposition - S2-E19
Continuity mistake: After the guys leave and Penny and Sheldon are eating alone, Sheldon's chopsticks switch between an unevenly broken pair of chopsticks and an evenly broken pair of chopsticks.
The Hofstadter Isotope - S2-E20
Continuity mistake: Near the end of a conversation with Stewart, Penny is holding a drawing that Stewart drew for her. In the next shot, it is now on the counter and she is picking it up.
The Vegas Renormalization - S2-E21
Continuity mistake: When Leonard and Raj are getting ready in the bathroom, Raj picks up a tube of shampoo/conditioner off the bathroom bench with his left hand. However, in the next shot, Raj has nothing in his left hand and the tube is back on the bench, with no time for him to replace it between shots.
The Vegas Renormalization - S2-E21
Continuity mistake: In the bathroom of the hotel in Las Vegas, we can see Rajesh taking a small white bottle and keeping it in his hand while saying "I love Las Vegas". In the next shot, the bottle has returned to its place instantly.
The Classified Materials Turbulence - S2-E22
Continuity mistake: In the comic book store, when Stuart and Leonard are talking about Penny saying "Leonard" when with Stuart, Stuart's pen/hand is constantly changing position instantly.
The Classified Materials Turbulence - S2-E22
Continuity mistake: When Raj is going through the ideas on what would work to fix the toilet, Sheldon's hand is not near his face, but when Howard talks about moving to Israel, Sheldon's hand is up by his face.
The Classified Materials Turbulence - S2-E22
Continuity mistake: Leonard is talking to Stuart at the door to his (Leonard's) apartment. Howard then comes over and slams the door in Stuart's face and Leonard has moved back about 4-ft instantly.
The Monopolar Expedition - S2-E23
Continuity mistake: When Penny finds out about the expedition, Sheldon starts to walk to his apartment. Camera cuts to Leonard in the apartment for five seconds and then to Penny in the doorway. Behind her, you can see Sheldon walking to the apartment still. Since he was halfway to start with, he should be in the apartment by now. (00:10:35)
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The Electric Can Opener Fluctuation - S3-E1
Continuity mistake: Sheldon's Sandwich goes from looking burnt to not burnt in the next few frames. (00:16:56)
The Gothowitz Deviation - S3-E3
Continuity mistake: When Penny is making French toast and Sheldon walks into shot, the edges of the toast are not covered in egg whilst the rest of the toast is. About 30 seconds later, Penny asks Sheldon if he wants French toast and the edges are still not covered in egg. The shot cuts to Sheldon. In this shot we can see Penny's hands to the far edge of screen and fully raised showing us that she hasn't dipped the edges of the toast in egg yet. But in the next shot, we can see the whole of the toast is covered in egg, including the edges of the toast that were clear a moment earlier. (00:00:20 - 00:00:50)
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The Creepy Candy Coating Corollary - S3-E5
Continuity mistake: At the dinner, Howard's mom calls. Howard's wine glass refills itself between shots. (00:15:20)
The Creepy Candy Coating Corollary - S3-E5
Continuity mistake: Bernadette speaks regular here. In future episodes she suddenly has a higher-pitched voice.
Suggested correction: This isn't really so much a mistake as it was a character tweaking, which happens often in TV series.