Deliberate mistake: When the chickens are first shown, one of them is upside down.
The Builders - S1-E2
Deliberate mistake: When Basil is arguing with Polly and eventually decides to call O'Reilly, he trips over the gnome. However when we see Basil come out from behind the desk, he takes the gnome out of a side gap in the desk, perfectly out of reach of Basil tripping over it. (00:14:30)
Deliberate mistake: The show is set in New York. Joey was a cast member on Days of Our Lives, which is filmed in Los Angeles, but is still always around.
Deliberate mistake: Lily was an infant for all of season 5, but beginning with this season, she is around 5 years old. The show didn't jump forward in time, because JT states in a season 5 episode that he is 19, and in the episode this season where he and Rich go to Mexico, he states that he is almost 20, as well as Al and Mark are both still in high school.
Mr. Monk Meets His Dad - S5-E9
Deliberate mistake: In the opening scene, Wood's tie is grabbed by an exposed fan belt located above the side of the engine. However, this belt/pulley assembly doesn't exist in a real truck's engine compartment - the fan belts are all in front of the engine, where the camera can't see them easily. The prop master must have added this dangerous device to the truck to allow the camera to see the strangulation.
Deliberate mistake: Hank only discovers the tattoo on the back of his head after having his hair shaved off. There is no way, however, he wouldn't have noticed it before this. The tattoo artist had to shave hair off the back of his head before putting on the tattoo. While he might have not realised right away, the pain the following day and the fact that he would have noticed a large part of his hair missing would make it unavoidable.
Twenty-something girls vs. thirty-something women - S2-E17
Deliberate mistake: In the scene at the beach party, when Carrie brings everyone beers, Miranda says "There's so much foam, I could ski on the head," but the cups are tipped toward camera and you can see there's no foam at all.
Deliberate mistake: After Barney buys the car from Mrs. Lesh, he and Andy are standing at the steps as he tells her not to look back at the car, and the next shot of Andy and Barney at the front door is the same shot from a few moments prior, but it's been flipped so they would be looking in the opposite direction. (00:09:30)
Boys in the Band / Hex Games - S2-E2
Deliberate mistake: When AJ and Chester show Timmy "The Timmy Tuck", AJ says it has a 1400 degree turn. The diagram shows 140°.
Deliberate mistake: Every time there is a scene on the beach, the background is so fake - the waves never move.
Deliberate mistake: While Bobby's parakeet is flying around downstairs, before the bird settles down on the TV set there are two closeups of Bobby which are flipped shots, note the furniture and Bobby's PJs. (00:07:00)
Deliberate mistake: Although it is later revealed that Sarah is the intruder, the person fighting is male.
The Anniversary Present - S2-E1
Deliberate mistake: In this episode Lucy is trying to get Ricky to notice that their anniversary is on Monday the 19th by showing him a large calendar with the 19th circled. However, when they are in California and they celebrate their anniversary and Ricky asks for information to be wired to him, the telegram tells him that their anniversary is on the seventh.
Deliberate mistake: Lindsay is not at Caleb's funeral in the last episode of season 2, "The Dearly Beloved". It's unlikely that she would have missed it - she is still on good terms with him and he is her father, the only reason she left was to be with her mother, not because she didn't love Caleb.Obviously they didn't want to create another drama with having Lindsay there while they had to focus on the important story-lines - Caleb's death, Kirsten's drinking and Marissa shooting Trey.
The Wedding - S4-E3
Deliberate mistake: In the scene where the tow truck guy crashes the car window, notice the glass goes in the car. Later the glass is there, but Josh sits in the car without being cut by it.
Open the Door Witchcraft - S1-E28
Deliberate mistake: Sam and Darrin are "trapped" in the garage; however, you can see a side door.
Deliberate mistake: In the first few series, it is suggested Lister and Kochanski barely know each other. In 'Balance of Power' Holly says that Lister has only ever spoken 173 words to her. However, by series 4 Kochanski is referred to as Lister's ex-girlfriend with whom he shared a relationship. In the series 4 documentary, Doug Naylor explains that Lister's attitude towards Kochanski was immature in the first series which is why they changed his back story from wanting to be with Kochanski to actually having been with her by series 4.
The Hot Tub - S7-E5
Deliberate mistake: When Elaine comes home and doesn't find Sean Paul there, she runs to her neighbour across The Apartment. The neighbour opens the door and stands outside it then the door slowly closes behind him. Suddenly, the door opens again with a swoosh without anyone being there. Because the camera switches angle right after this, it is apparent it was opened to gain this shot or to at least permit it continuity wise. (00:16:40 - 00:17:10)
The Trouble With Trillions - S9-E20
Deliberate mistake: When Homer is being interrogated by the IRS, his package is briefly replaced by a ball of string when the IRS agent sits down in the chair and spins around.
Deliberate mistake: In this episode, Ray tells Amy's mother that Debra no longer reads his column, although she did when they were dating "and she was wooing me." But in an earlier episode, Ray proposed to Debra in his very first column - so when they were dating, he didn't have a column.