The One Where Monica Gets a Roommate - S1-E1
Other mistake: When Rachel arrives at Central Perk, Monica introduces her to everybody, including to Chandler, as if they don't know each other. In later episodes, we learn that Chandler met Monica and Rachel a couple of times when they were in high school (including when Monica cut his toe off). Chandler even kissed Rachel once, and since Chandler always says that he hasn't kissed many women, he should have perfectly remembered Rachel, and Monica should have remembered that the two of them knew each other. (00:04:40)
Suggested correction: Chandler and Rachel never really knew each other well. Chandler will have been in her mind as that guy that her best friend's brother hangs out with, and Chandler will only know her as the friend of his friend's sister. I doubt they'd remember each other as the kiss they shared was when she was drunk, and they didn't see each other for 6 years while Rachel lived a richer and dependent on her father type life.
The One With The Metaphorical Tunnel - S3-E4
Revealing mistake: While Chandler and Janice are in D'Agostino's, some grocery products have their names partially covered, such as Uncle Ben's and Grape Nuts.
Suggested correction: I've seen a few of these listed as errors, but they're not. A lot of shows do this often if you pay attention. It's called "product displacement", and it is done to avoid being sued or having to pay licensing fees. Also, it is cheaper to alter logos like this than pixelate/blur them out. What is interesting though, is that one of the grape nut boxes in this picture does not have an altered logo.
Yes, it's product displacement, and this is specifically referred to as the "greeking" process. However, your correction only offers an excuse as to why this occurs. The tape or paint partially or fully covering the brand names or logos are a distraction, and it removes viewers from the fake reality of the show or movie. Originally, these types of submissions were to be listed in trivia, but instead they were placed in the mistake section.
Trivia: The artwork on the wall behind the couch in the coffee house changes every 6 episodes.
Suggested correction: That's not really trivia nor a continuity mistake. Small businesses, particularly cafes and coffee houses, often show different local artists' work on a rotating basis in an effort to support the local arts.
The One With The Girl From Poughkeepsie - S4-E10
Factual error: Ross falls asleep on the train and ends up in Montreal, where the woman he meets tells him "it's only a 2-hour ferry ride to Nova Scotia." Yeah, more like a journey of between 13 hours (12-hour car ride plus 1-hour ferry) and 23 hours (multiple bus legs plus 1-hour ferry.) The character could have been lying to Ross, but it's not presented that way at all.
The One With The Embryos - S4-E12
Character mistake: After the guys have beaten the girls in the quiz, Rachel refuses to move apartments and Monica says: "If we had lost, we would have made them get rid of the birds." But they did lose. That's why the guys have got their apartment. She should have said if we had won.
The One Where Monica and Richard Are Just Friends - S3-E13
Factual error: Joey refers to several of his favorite parts of The Shining in 'code', including "all blank and no blank makes blank a blank blank, " which obviously refers to the "all work and no play makes Jack a dull boy" scene from the movie. However, that scene (and the one where Danny sees the two "blanks" in the hallway) is not found in the book; only in the movie. (00:13:55)
Suggested correction: I know they're talking about the book, but doesn't it actually make sense for Joey to be referencing the movie, even though the conversation is about the book? Considering the character, I don't think that's off at all. He's read the book, but he's obviously seen the movie, too.
Later in that scene, Ross references The Shining as a book Joey loves that stars Jack Nicholson. Therefore, it's safe to assume that Joey has seen the movie and the audience could infer that he may confuse the two often enough for Ross to reference it that way. This might just be another Joey mistake (which he has many) vs a factual error of the show.
The One With Monica's Thunder - S7-E1
Audio problem: When Joey walks out of the bedroom dressed as a 19 year old, when Chandler says the line "Yes, on a scale from 1 to 10, 10 being the dumbest a person can look, you are definitely 19", you can see that the audio doesn't match the words. It looks as though Matthew Perry says "not 19" and they had to re-dub over post production with "19." Subtle, but it's there. (00:08:50)
Suggested correction: Just watched it twice and seems to be fine... Can't see any issue.
The One In Barbados, part 2 - S9-E24
Character mistake: When Monica and Mike are playing table tennis, Monica puts her hand on the table and looses the point. Mike then does the same thing. Surely Monica, of all people would notice that as it would have given her the point. We also see her looking at Mike at the time. (00:33:40 - 00:39:25)
Suggested correction: Not really a mistake to not notice it, especially when it may be what a character like Monica would notice. She is being extremely competitive and frustrated because Mike just denied her a point, so it's fair to say human nature plays a part here.
The One With All The Thanksgivings - S5-E8
Other mistake: When Joey comes out the bathroom in the girls' apartment with a turkey stuck on his head, the bathroom floor has the black and white tiles. But that floor wasn't there until Joey put it there in Series 3, The One With Frank Jr. So in the flashback the bathroom floor should be white tiles. (00:04:45)
Suggested correction: Joey said in the Frank Jr episode that the tiles used to be a different colour. The thanksgiving flashback was in 1992 so something must have happened to the bathroom floor tiles in the time gap between 2 years before the series started and three years after it did.
The One With Rachel's Other Sister - S9-E8
Revealing mistake: When Chandler grabs his bag he accidentally lets the box full of wedding china fall off the stool. Watch closely (play in slow-motion). The box falls on the floor and shattered china falls out. The china was ALREADY broken before it falls on the ground. (00:23:00)
The One with the Dozen Lasagnas - S1-E12
Revealing mistake: After Phoebe tells Rachel that Paolo made a pass at her, we see a shot of the outside of Monica's apartment block and Rachel is throwing Paolo's clothes out of the window. Look closely and you can see the clothes have been very badly superimposed on to the background. (00:17:05)
Suggested correction: The show sent a crew to New York to film the clothes being thrown from the same building that is used in establishing shots. In a wide-screen version of the episode, the clothes can be seen being thrown out a window (although in the episode the clothes are supposedly thrown off a balcony).
The One Where Rachel Quits - S3-E10
Continuity mistake: At the start of the scene in which Ross breaks the little girl's leg, we can see that the stairs are just separated by railings. Later in that scene, when Ross and Chandler start walking up the stairs, there are walls on both sides of them. (00:01:40)
Suggested correction: This isn't completely true. In the first shot, we see railing in the middle, as shown in the screenshot. Then, the shot changes to upstairs, looking down, and we can see the wall, as shown in the bottom picture. However, at the end of the wall, it goes into the railings, which is visible just as the pair start to climb the stairs. A screenshot of this can be seen here: https://ibb.co/bmZ8xTc, making it easier to understand.
The problem with the screenshot is the right side is circled to show there's no railing, but the railing is on the left side (to the character's right), but Chandler is blocking the view of the railing. Ssiscool's screenshot is before Chandler starts to walk up the stairs, which is why it's seen.
The One With Joey's Porsche - S6-E5
Revealing mistake: When Phoebe knocks over the vase she glances at it just before throwing the diaper. (00:15:10)
Suggested correction: The bin for the diapers is near the vase, and she glances at that before throwing the diaper.
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Rachel is telling Ross why she doesn't want to go to the dinner, and she says "the first sign is I don't want to, and...I'm not going'. While she says this, her left hand is completely empty, but then in the next shot the camera goes back to Ross and she is now holding the baby monitor in that hand. It then moves around in different shots afterwards. (00:06:10)
Suggested correction: She comes in with that baby monitor and it never leaves the sight of camera.
The One Where Ross Got High - S6-E9
Audio problem: When Ross and Joey go into the bedroom, you can hear the duck in the background, even though the chick and the duck should be in the other apartment and aren't even in this episode. (00:12:53)
Continuity mistake: After Chandler makes the joke about Joey cracking show business, Joey is holding the phone in his left hand. In the next shot, it is in his right hand. (00:11:20)
Suggested correction: You can actually see him switch it to the other hand before the next scene pops up if you look close enough.
Not for the shot the mistake is talking about. Throughout the scene he's switching the phone back and forth. But after Chandler's line, Joey is just standing there with the phone in his left hand, he doesn't make any move to switch hands. In the next shot, the wide shot from the side showing everyone, you see the phone is in his right hand.
The One Where Underdog Gets Away - S1-E9
Continuity mistake: At the end of the episode when Chandler makes a toast, he is holding the glass in his right hand. In the next shot, the glass has jumped to his left hand. (00:21:05)
Suggested correction: He switches the glass from right to left, so, unfortunately you're wrong.
The mistake is valid. While we do see him switching his glass between hands during the scene, when he says he's glad everyone's Thanksgiving sucked, he raises his glass in his right hand. In the next shot it's switched to his left and lowered a bit. Since this happens between shots (and he's not off camera), it means no time elapsed, so there's no time for him to switch hands again (in the submitted pictures, the bottom picture is the first shot and the top picture is the 2nd shot).
The One With The Worst Best Man Ever - S4-E22
Other mistake: Given her vegetarianism, and her disdain for fur in another episode, there's no way Phoebe would have wanted a pair of leather pants.
Suggested correction: It's your opinion that Phoebe wouldn't have wanted leather pants, but that's not true of all vegetarians. Natalie Merchant was known for saying she was a vegetarian but still wore leather shoes. I was a vegetarian who would never have worn fur and still wore leather shoes.
The One With Joey's Big Break - S5-E22
Other mistake: When Ross is questioning Phoebe on why she is mad at him, he has his blue sweater on backwards.
Suggested correction: So he has his sweater on backwards. That's a character mistake, not a movie mistake.
The One With Ross's Inappropriate Song - S9-E7
Other mistake: When Chandler finds out that the video marked 'Monica' is just a football game he says, 'This may be the first time I have enjoyed football.' Although in 'TOW The Football' (season 3) he is quite happily watching the Thanksgiving Day game with Ross and Joey.