The Robotic Manipulation - S4-E1
Continuity mistake: When Penny says "let's just finish our dinners" she raises her fork twice. (00:16:45)
The Zarnecki Incursion - S4-E19
Character mistake: As they drive to Todd Zarnecki's to confront him, Sheldon says, "I almost feel sorry for the poor fool, sitting in his split-level suburban ranch..." Architecturally, split-level (technically three levels joined by half flights of stairs) and ranch (single level) are separate and distinct designs. There is no "fusion" of the two. I can't help but think Sheldon would have corrected anyone who said the same thing.
The Justice League Recombination - S4-E11
Character mistake: Even with Penny and Zack the guys are one man short to be the original JLA because they they don't have the Martian Manhunter. If they used the same costumes in the previous year, they would have been three people short of the original line-up.
The Prestidigitation Approximation - S4-E18
Continuity mistake: Near the end of the episode, in the canteen scene, Howard shows the card trick to Sheldon again. The card at the bottom of the deck is the 2 of hearts as he takes them from the box. Sheldon then takes this card from near the top of the deck when Howard puts them on the table. The deck is not shuffled between times.
The Robotic Manipulation - S4-E1
Continuity mistake: The lemon wedge in Amy's water flips back and forth throughout the dinner scene. (00:17:00)
The Hot Troll Deviation - S4-E4
Continuity mistake: When Leonard and Howard are talking at the University, Leonard says "Oh my god you ran over a hobo!" when he does so Howard is not holding his fork, camera cuts and he suddenly has his fork in his hand. (00:05:15)
The Apology Insufficiency - S4-E7
Continuity mistake: When Sheldon is drink his shots, the amount in his shot glass increases before he takes final shots.
The Robotic Manipulation - S4-E1
Character mistake: While driving towards the restaurant, Amy mentions she uses dandruff shampoo for her "dry" scalp. Dandruff and dry scalp have the same main symptoms, which are falling flakes and an itchy scalp, but they are two different conditions. In dry scalp, the skin gets irritated and flakes off. With dandruff, the cause is too much oil on the scalp. That excess oil causes skin cells to build up and then shed. Therefore dandruff shampoo should be used for an oily scalp, not a dry scalp. (00:11:19)
Suggested correction: Except there are dandruff shampoos that specifically treat dry scalp. In addition, dry scalp is commonly caused by dandruff.
More of a continuity error regarding this is that much later she claims that lice isn't attracted to her hair cos of her naturally oily scalp (contradictory).
Then that should be entered as a mistake. What was entered isn't a mistake.
The Robotic Manipulation - S4-E1
Continuity mistake: At the start, as Howard says "And finally my kung pow chicken" the robot arm is level with the top of the bag. Camera cuts and it's reaching to the bottom of the bag. (00:00:15)
The Hot Troll Deviation - S4-E4
Continuity mistake: When Sheldon and Raj are arguing about having a desk in Sheldon's office, Sheldon's bottle of water keeps rotating without anyone touching it - take note of the label. The level of water in Sheldon's drink also keeps changing between shots. (00:06:20)
The Robotic Manipulation - S4-E1
Continuity mistake: When driving to the date, the cars behind Penny's change place instantly. For example a 4x4 becomes 3 cars, which become 1 car in the space of 3 seconds. (00:09:10)