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.
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 Countdown Reflection - S5-E24
Continuity mistake: Near the beginning of the episode, Howard said the launch was on the Friday before his planned wedding. They decide to marry before he launches, and they say they only have two days. Then he tells the clerk at City Hall that he launches on that Sunday. Too many inconsistencies.
The Countdown Reflection - S5-E24
Other mistake: Raj doesn't get over his selective mutism until the end of season 6. However, he very prominently speaks during Howard and Bernadette's wedding without alcohol or meds. In the season 6 episode where he finally does speak without any assistance, Penny makes a big deal about it so it's shocking when he does it here with no big shocks.
The Friendship Contraction - S5-E15
Character mistake: Sheldon told Leonard at lunch that they were no longer friends, only roommates but later that day, he told start moved up to ninth place on his friends list because he dropped someone (can't remember who) off his friends list). In actuality, it would've bumped him up to eighth place because he kicked Leonard off the list.
Revealing mistake: Any time that Leonard is "driving" his hands never move and the wheel never moves either.
The Consummation Deviation - S12-E8
Continuity mistake: Leonard tells Raj that the first sex between Penny and Leonard was fantastic. But episode S3E2 is all about how bad it was.
Other mistake: Leonard says that it's 2am when his door is knocked on, but when he opens his door to confront Sheldon, his window outside shows daytime light. (04:12:00 - 04:25:00)
The Euclid Alternative - S2-E5
Revealing mistake: When we see Sheldon and Howard on the scooter, look in the back of the mirrors to see the reflection isn't moving. Indicating the bike isn't moving. (00:07:40)
The Imitation Perturbation - S12-E6
Continuity mistake: When Bernadette and Amy are sitting in the kitchen, the teabag in Bernadette's cup changes position between shots.
The Launch Acceleration - S5-E23
Factual error: In all the episodes leading up to Howard and Bernadette's wedding, Howard was going into space to install a space toilet. But in this episode, Howard tells her they want his telescope, so he has to go.
Suggested correction: The space toilet was something Howard designed that NASA installed back in season 2. His mission to the ISS in season 5 was always about his telescope. In episode 5, "The Russian Rocket Reaction", Howard says NASA picked his team's design for the deep field space telescope that's going on the International Space Station in the spring.
The Proton Displacement - S7-E7
Character mistake: When Raj shows Penny, Amy, and Bernadette how to make jewelry, Penny keeps having trouble with the glue and gets it all over her fingers. However, in Season 2, episode 5, she has no trouble at all with the glue when making 1000 Penny Blossoms.
The Speckerman Recurrence - S5-E11
Character mistake: Throughout the show, Sheldon denounced his mother's religion and God. To the extreme. In this episode, he said, "More sense than God gave a mouse." He would never invoke God for any reason.
The Big Bran Hypothesis - S1-E2
Character mistake: Sheldon does not do his 3x OCD knock on Penny's door.
Suggested correction: That quirk wasn't brought into the series until halfway through the first season. The one-knock Sheldon happened a couple of times before it became the three knock habit.
The Creepy Candy Coating Corollary - S3-E5
Other mistake: When Sheldon signs the entry sheet Stuart claims he wrote "Die Will Wheaton Die." But he was only writing for half a second to a second, he could never have written all that in the time frame.
The Prestidigitation Approximation - S4-E18
Continuity mistake: It is well-known that Leonard's glasses do not have lenses to avoid catching reflection by the lights. In this episode, Priya takes Leonard's glasses off, and they have lenses.