Continuity mistake: When Lily is selling her favourite dress and is saying how she got a two syllable damn, the flashback shows her with the hairstyle she got after Coming Back from San Francisco, even though she said it happened in 2004. She should have had her shorter, lighter coloured hair. (00:15:10)
Continuity mistake: When Robin leaves to get Battleship, Barney thinks they're going to have sex, whips his belt off, and throws it on the floor. When Robin returns, he's neatly folding his pants and draping them over a chair, and his belt is still threaded through the loops. (00:16:20)
Suggested correction: He could have easily done that himself so it was easier to put back on afterwards.
This correction is too much of a stretch. It would make no sense for him to take off the belt and throw it to the ground in the first place. He was alone at that point, so he wasn't doing it to impress anyone and he's been in this position before.
Continuity mistake: When Barney is in the Professor's office, we see the professor put a red pen down on her desk and her hands are then empty. In the next shot, she suddenly has a blue pen in her hand.
Continuity mistake: When Lily and Marshall are talking in the kitchen, we see Lily put down the recipe card to the left of the jar of mayonnaise. The shot changes and the card is now to the right of the jar. (00:06:25)
The Pineapple Incident - S1-E10
Continuity mistake: When Marshall gives Ted the phone to find out who's number is on his arm, he presses 2 buttons then gets through. No time to dial the number. (00:12:00)
Slapsgiving - S3-E9
Revealing mistake: When Marshall slaps Barney in Slapsgiving you can see that his hand doesn't actually touch Barney's face and there is no audio to match the slap.
Other mistake: In the flashback where Gael is playing a guitar and singing a song, the chords on the guitar change, but his fingers do not move at all. He is playing the same chord the whole time.
Matchmaker - S1-E7
Continuity mistake: At the Matchmaker's office, when Barney is saying he just wants someone to hold, Ellen is seen putting her pencil down on the desk but in the next shot it is in her hand again. (00:03:50)
Sandcastles in the Sand - S3-E16
Continuity mistake: When Lily goes to the bar with her friend Michelle, Barney says "I want her around all the time." It then cuts from Barney to Lily's slightly shocked looking face, obviously from a previous cut/scene change, sitting at the table with them - she should still be walking to the bar with Michelle.
Suggested correction: Those were different days. Robin agrees to watch Simon's practice before we see Michelle the first time, then the scene cuts to Robin watching the band practice, then the news feed and then the next scene with Michelle. All the character's clothes changed indicating a different time.
Factual error: The way Barney employs the green screen wouldn't work because a camera is needed to put a picture over the screen. To the naked eye the screen would still be green. The only plausible way to make the illusion work as intended would be a regular white screen and a projector, but this isn't the case here.
Continuity mistake: The morning after the second party, the items on the coffee table change instantly between shots. Several beer bottles and blue cups vanish, whilst a red cup and red bowl appear. (00:11:00)
The Wedding - S1-E12
Continuity mistake: In this episode, Lily is in Robin's house with her dogs. In the episode "World's Greatest Couple", Robin reveals that Lily can not stay at her apartment because Lily is allergic to dogs.
Suggested correction: Doesn't mean Lily can't go over and visit for a while. My mother is allergic to cats. She can visit her cat-owning friends for a while, though she would never stay overnight. Pet allergies can be pretty controllable, as long as you're not constantly in contact with the animal.
Continuity mistake: When Steph is telling Ted that she used to star in adult films, we see her pick up the mini corn with her chopsticks from one angle, then the shot changes and she picks it up again. (00:02:30)
Continuity mistake: In the final scene at the bar, Barney is seen eating the olive from his drink and discarding the stick. A second later, when the shot changes, the olive and stick are back in his glass.
Plot hole: When Robin and Lily find Barney's secret Robin notebook, Barney and Ted are at the class, so Barney should have the notebook with him.
Suggested correction: This is a character mistake at best, and quite a common one. Students constantly forget their textbooks, homework, notes, supplies etc.
It should be noted that the plot hole isn't talking about "students." This isn't about forgetting textbooks, supplies, or homework. Barney is trying to be a better boyfriend to Robin and wants to learn Ted's secrets since Ted had dated Robin. If Barney has been writing everything down before, the mistake is pointing out why isn't he writing it down this time, except to allow the writers to have Lily and Robin find the notebook and the class.
Revealing mistake: In the big song and dance number, during the line "Girls will go and girls will come, but there's only one absolute", one of the dancers in the second line that runs in from the right is wearing trainers, not dress shoes.
Other mistake: When Ted and Robin borrow Marshall's Fiero and are sitting in the car talking as Ted drives, you can hear the beat of a song playing in the car that is not the Proclaimers' I'm Gonna Be (500 Miles), which in many future episodes is referenced as the only song that can be played in that car due to the tape being stuck in the tape player. (00:15:30 - 00:16:10)
Suggested correction: Maybe it's on the radio.
