Character mistake: When Ryan is recreating the chess game he and Mandy played, he has the chessboard setup incorrectly. He has the dark square on the lower right corner when it should be the white square. He was a junior grand master and would know better, especially since he had the board set up correctly when they were playing.
Looking for Mr. Goodbrain, Part 2 - S3-E13
Character mistake: When Liv and Clive are talking to Chase about Katty, Liv tells Chase he had a cocktail napkin with Katty's phone number on it. However, it was only Katty's hotel room number that was on the napkin, which Liv saw.
Character mistake: Lorraine mistakenly tells Denny to "call 999" instead of 911, and when asked about it by Katie, denies having ever spent time in the UK (later revealed to be a lie). But this isn't some high-pressure slip of the tongue, she's highly intelligent and has been in America for a decent length of time, is working hard to maintain her facade of being born and bred American, so there's no way she'd slip up over such an obvious thing.
Character mistake: In the Armchair Theatre story, Billy mentions that the grandma puts a tray of chocolate brownies into the oven. In the next scene the grandma (played by Billy Butler) has a tray of cookies, not brownies.
Cat on a Hot Steel Beam - S1-E60
Character mistake: As the fire truck darts out from a back alley, the sign on a nearby gift shop window reads "gift's" when it should be "gifts".
Character mistake: When Tam shows off his GFT Platinum Pass to Jack and Victor, it reads as 'Plantinum Pass'. (00:06:29)
The Hairy Scare of the Devil Bear - S1-E8
Character mistake: Velma says bears only have four claws. Wrong, they really do have five claws.
Character mistake: When talking about poker Jimmy asks Dave "What are the chances of getting five of a kind of the same suit?" The most you can get is four of a kind and they would be all different suits.
Suggested correction: Jimmy says "in the same suit" which is slightly different than "of the same suit." It was just a weird way of saying the odds of getting a flush. Lisa replies with 504.8 (the odds of getting a flush). In poker lingo, 3 or 4 of a kind is taken to mean same value since 3 or 4 cards in the same suit isn't anything.
Suggested correction: Five of a kind is possible when using one or more wild cards, such as Jokers.
Character mistake: Lucy Liu-bot says Fry's name normally, but uses an automaton voice for "Can eat more", when she has always used Fry's name as a Text-to-speech type of automaton voice. (00:07:45)
Character mistake: In Season 3, Episode 10 (Careers), Leonard admits to being a beginner at bicycling. Then, he proves it by having his helmet mirror on the wrong side.
The Wedding - S8-E23
Character mistake: When Roseanne, Darlene, Jackie, Bev, Becky, and Nana Mary are dressing for Darlene's wedding, Nana Mary comments that all of them were pregnant when they married. However, Becky, was not pregnant when she and Mark eloped and they never had children together. Roseanne was not pregnant before marrying Dan. When the series began, Becky was 13 years old and Dan and Roseanne had been married 15 years.
Character mistake: In "Movie Maniacs," the Three Stooges arrive in Hollywood via train, sneak into a movie studio and walk onto the set of a movie being filmed. A starlet looks at Curly and says, "Oh, Mr. Howard." There is no way she could have known his name.
Lady Florence Craye Arrives in New York (or, the Once and Future Ex) - S4-E2
Character mistake: Cheesewright is trying to convince the police to raid the charity ball because alcohol is going to be served. The police chief tells him they stay out of private affairs and Cheesewright replies "The law's the law!" Prohibition made illegal the sale and transport of alcohol, but people were still allowed to have it in their homes or private functions. No laws were being broken. (00:33:30)
Character mistake: Jessie's dance moves don't match what the other girls are performing, even though it's a choreographed routine.
Character mistake: Edith says in a story that Archie has a brother Phil. In actuality Archie had 1 brother, Fred.
Character mistake: When Rarity sees her cat stuck in the tree, Rainbow Dash is sitting next to the cat, but when you see her, her cutie mark is not there. (00:17:15)
Character mistake: While filming the cheerleader performance, Jasper refers to his inability of using computers ("We're gonna put this on YouTube as soon as one of us figures out how to use a computer!"). Earlier in the series, however, Jasper ordered himself a Russian wife online, so this statement is definitely off-character.
Character mistake: When Matt is telling his Dad about his problems, he says "...I kicked our social studies globe last week by accent." He should have said accident; although this is not a major error it is worth noting and looking out for. (00:03:35)
Who Was That Baby I Saw You With? - S3-E7
Character mistake: After the mixup where a baby's grandmother took baby Andrew instead of her own grandson, in trying to track her down, Muriel mentions how since it was the baby's grandmother (instead of a parent), it would be hard to track her down because her last name would be different from her grandson's. This is not fully correct. Generally a baby will have a different last name than its MATERNAL grandmother, but the same last name of its PATERNAL grandmother, so Muriel's comment was only half accurate.
Character mistake: The leader of the Purple Knights says that they would only be bike riders if they couldn't tell which gender someone was by their hair. This is a major mistake, because if you look at the hair of the Purple Knights, it's incredibly easy to tell which gender someone is.