The One with the Monkey - S1-E10
Continuity mistake: When David kisses Phoebe in the lab the first time, he writes "yes" on the board. Later on when they are in the lab again the "yes" is different than the previous one.
The One With Ross's Wedding, part 2 - S4-E24
Audio problem: Toward the end of the episode Ross' Dad and Emily's dad are arguing. Ross comes between them and you can hear the audio saying"From now on everybody gets along!" But it does not match up with the movement of Ross' lips.
The One Where Ross Hugs Rachel - S6-E2
Visible crew/equipment: After Ross tells Phoebe that he does not have feelings for Rachel, just as Ross walks into the apartment to find Rachel crying, the shadow of the moving boom mic can be seen on the wall at the top, left side of the screen. (00:20:15)
The One With Ross and Monica's Cousin - S7-E19
Continuity mistake: When Monica comes into Phoebe's apartment for her Surprise Bridal Shower, the view of the hallway outside the apartment is a dead end on the right side (the left side cannot be seen), however, in S7:E12 (The One Where They're Up All Night), both when Phoebe is disposing of the fire alarm and when the fireman is at the door, it is clear that there is another apartment opposite hers, as well as a trash chute on the right side. (00:18:25)
The One With The Truth About London - S7-E16
Revealing mistake: When Monica gives Phoebe the headache medication (Hexadrin) she, not only doesn't take the lid off - and therefore fails in pretending to put it back on - but also doesn't actually give Phoebe anything. Extended episode. (00:07:30)
The One Where They're Up All Night - S7-E12
Revealing mistake: When Chandler is getting a pan out to warm some milk, he successfully pulls the bottom pan out without too much disruption, however, the joke (and entire plot device - to wake Monica up) is to make as much noise as possible so Perry pulls out more pans on purpose and knocks them on the floor. This is quite clear - you can see him grasp the wok and pull it out onto the floor. (00:06:30)
The One With All The Haste - S4-E19
Factual error: The guys are gone for a single night, watching the Knicks game. (You can tell this because they talk about how "we can go see the game tonight," and when they get back everyone's wearing the same clothes as that conversation.) When they get back, both apartments are completely switched back: the large, heavy furniture is replaced, the posters are re-hung, etc. Even if they were gone from, say, 6 p.m. to midnight or so, there is no way that Rachel and Monica would be able to make that transition in that kind of time.
The One With The Embryos - S4-E12
Character mistake: When they are about to start the game, Ross declares that "the first team to answer the most questions wins." This is a nonsensical statement. By that logic, the first team to answer a question correctly would be the winner. It should be either the team that has correctly answered the most questions at the end of the game wins, or the first team to correctly answer an X number of questions.
Suggested correction: While it's a weird way for him to say it, he starts by saying "each team will answer ten questions", so no, the first team to answer a question wouldn't win.
Yes, he qualified that it was a 10-question game, and we as the audience understand going in how the winner is decided. It's just the way he declared how the winner would be decided didn't make sense. It would be like watching an NBA game, and before tipoff, the crew chief tells both teams that the first team to score the most baskets wins. We know what the rules of an NBA game are, but the referee makes a nonsensical statement all the same.
Except there's so many variations of how a team can win a game; best 3 out of 5, win by 2, or a game can even end in a tie. Since this isn't a professional sport where all the players know how a game ends, Ross is basically saying after 10 rounds, if there is a tie, it will go to sudden death with the team with the first correct answer winning, just not in so many words.
The One with the East German Laundry Detergent - S1-E5
Character mistake: Janice enters Central Perk with a large shopping bag and even shows Chandler what she bought but when she leaves a few hours later, she leaves without it.
The One with the East German Laundry Detergent - S1-E5
Revealing mistake: When Ross and Rachel are looking at the pink clothes in the washer, it's clear the clothes are actually dry. (00:17:20)
The One with the Blackout - S1-E7
Other mistake: Ross says that he was at Disneyland with Carol and got caught hooking up on Small World and asked to "never to return to the Magic Kingdom." Disneyland is in California and the Magic Kingdom is part of Disney World in Florida. (00:06:10)
Factual error: This is a mistake for two of Ross' three marriages. Ross wasn't even actually "married" either time. With Emily, he goes through the ceremony of the marriage and then Emily immediately disappears. You're not actually married until the certificate is signed and sent in, with the signatures of the witnesses. Which was not happening after that disaster of a wedding. Nor were there any witnesses filling out and sending in certificates after the drunk Vegas wedding either.
Suggested correction: The certificate of marriage is signed and sent in by the person performing the ceremony, and he asked if they wanted to continue with the marriage and it was completed. Secondly the marriage to Rachel they discuss how they paid witnesses to the wedding. I believe they mention Elvis?
Suggested correction: At the Vegas wedding, the chapel likely provided witnesses who took care of the paperwork.
The One After the Superbowl, part 2 - S2-E13
Revealing mistake: Rachel grabs a jar of sauce from the shelf and says, "You give me back my sweater or it's handbag marinara." You can tell from the sound it makes when it opens - no pop - that the jar had already been opened before she pulls the lid off.
Factual error: When Bonnie shaves her head, Rachel is supposed to have given her the razors (according to Bonnie.) Nope - the kind of razors needed to do that kind of close shave are a very particular kind, and Rachel isn't going to have them unless she also shaves her own head. It also wouldn't make any sense for Bonnie to have used her own razors; she's not going to carry them around with her unless she's planning to use them.
Suggested correction: Considering Bonnie always used to shave her head, it's not beyond the bounds of possibility that she just kept a razor on her in case she wanted to do it again. She's an impulsive type of person, after all.
The One With The Dollhouse - S3-E20
Other mistake: The dollhouse is only partially burned when Ross takes it into the bathroom to extinguish it. When he shows it to Phoebe it's completely blackened and destroyed. He and Monica wouldn't have just let it burn; they would have extinguished it ASAP, and there's no reason why that wouldn't have been fast if they doused it in the shower.
The One Where Ross Dates a Student - S6-E18
Other mistake: Ross' semester supposedly just ended, and he's handing in his grades. But the episode just before this one was about Valentine's Day, and the one immediately after this one is about spring break, so this episode is happening sometime between mid - February and March/April. It doesn't matter when the show was aired or produced; Valentine's day is still in February. There's no semester that ends at that time of the year, and NYU wasn't on the quarter system then.
Suggested correction: This episode (production code 225567) was produced before episode 17, "The One With Unagi", (production code 225568) and just aired out of order. So this episode happens before Valentine's Day.
The One Where They All Turn Thirty - S7-E14
Plot hole: There's no way Phoebe has lived to 31 without knowing her birth date. She's had "real" jobs (like the massage parlor) and those require social security numbers and accurate birth dates. She didn't go to high school, but she mentions classmates, so she must have gone to elementary/middle school, and those required birth dates even in the '70s and '80s. She's also "lived in Prague," which she couldn't have visited without a passport - which requires a birth certificate.
The One with the Blackout - S1-E7
Other mistake: When Ross and Rachel are out on the balcony alone for the first time, there are no lights on in NYC apart from candle lights. Look in the BBQ behind them though to see a very bright and very white light reflected in the paintwork. (00:13:50)
The One With All The Kissing - S5-E2
Continuity mistake: A few days after the friends have returned to New York following Ross' wedding, Monica's hair is suddenly about three inches longer and a completely different style than it was in London. It was previously just above her shoulders in a sleek "pageboy" style. Once back home, it is much bushier and longer, well over her shoulders. This was obviously due to Courtney Cox growing her hair during the break in-between Season 4, which ended with the Ross/Emily wedding debacle, and Season 5. (The first episode of Season 5 was filmed the previous season and was Part 2 of Ross and Emily's wedding).
Character mistake: Even though both Ross and Rachel have cell phones with them and use them for other calls, it never occurs to Ross early on and as he's frantically racing to the airport with Phoebe, to call and tell Rachel that he loves her or at least to say that he is on his way to tell her something important before her plane takes off for Paris.
