Revealing mistake: Before Phoebe agrees to carry Frank and Alice's' triplets, she already has a baby bump.
Continuity mistake: In the early episodes there is a wooden post in front of the door at Monica's apartment. Remember when Monica and Rachel were looking after Ben and Monica bangs his head - Monica shouts "Monica bang" and runs into it. The post doesn't appear in later series. This was due to the post being an obstacle to shoot around.
The One With The Metaphorical Tunnel - S3-E4
Continuity mistake: When they are in the coffee house talking about the fact that Joey missed his audition, Phoebe says, "And that is why we don't invite you to play." Her hands are at chest height, but in the zoomed out shot, they are lowered. (00:02:50)
The One with the Sonogram at the End - S1-E2
Other mistake: At the beginning when you see outside the museum, there's a man in a red t-shirt looking at the camera. (00:01:50)
The One After Joey And Rachel Kiss - S10-E1
Visible crew/equipment: After the gang leaves Rachel's room, right after she asks Joey "Are they right?", if you look above Joey's head, for a split of a second you will see a boom mic. (00:09:25)
The One With Rachel's Crush - S4-E13
Continuity mistake: At the start of this episode when Rachel comes in, you can see a bit of wooden floor by the door (carpet's visible in other shots). However, Monica doesn't pull up the carpet until later in the episode, after the apartment's tidier. (00:02:10)
The One Where Ross Got High - S6-E9
Factual error: A really picky one: When Ross looks at the recipe book, he says Rachel's made 'half a Shepherd's Pie'. Technically, a Shepherd's Pie is made with lamb, whilst it's a Cottage Pie that's made with beef (although the two names are often interchanged).
The One With All The Thanksgivings - S5-E8
Continuity mistake: When Phoebe is trying to turn on the TV, her necklace moves without her touching it. (00:00:15)
The One With The Metaphorical Tunnel - S3-E4
Continuity mistake: The position of the lid of Janice's box of contact paper changes repeatedly and after she tells Chandler she doesn't know what to say, she begins to slide the roll of paper back into the box. In the shot from behind, the box is closed. (00:09:50)
The One With The Apothecary Table - S6-E11
Continuity mistake: When Chandler says "Oh, just like the apothecary table of yore," Monica turns her head toward him twice. (00:02:30)
The One With The Fake Party - S4-E16
Continuity mistake: When Rachel is in her bedroom dressed as a cheerleader with Joshua, the sleeve of her sweater on her right arm keeps moving up and down. (00:15:00)
The One After Joey And Rachel Kiss - S10-E1
Continuity mistake: At the end of this episode, Ross enters the door of Joey's apartment and finds Rachel and Joey kissing. Rachel says "I'm so sorry". The next episode, The One When Ross Is Fine, shows the same scene but it has been changed: Rachel never says "I'm so sorry". Joey starts talking when Ross enters the room.
The One With The Birth Mother - S10-E9
Audio problem: When Monica and Chandler are talking about telling Erica, when Monica says "Technicality!" It doesn't match with her lips. (00:15:30)
The One In Massapequa - S8-E18
Continuity mistake: In The One In Massapequa, Jack Gellar is eating food off a stick. When he finishes he holds the stick while Rachel asks Jack if he has any pearls of wisdom. We can see the stick over Judy's shoulder. In the next shot the stick is gone from his hand, then we see Judy put it down on a table, then it reappears in his hand, before disappearing for good. (00:05:05)
The One With Ross's Wedding, part 1 - S4-E23
Plot hole: The wedding is threatened because Ross, Emily, and Monica discover that the location has been torn down a few days early. However, when one plans an event, especially a wedding, one puts down a deposit to hold the location, signs a contract, and has all of that in writing. The church would not have allowed the tear-down to happen early as they'd be in breach of contract for accepting money and then allowing the church to be torn down before the wedding. And if they had broken the contract, Monica would have been screaming about it and demanding a refund.
The One With Ross's Grant - S10-E6
Visible crew/equipment: When Dr.Hobart enters the meeting room to conduct the grant interviews, markers can be seen on the floor around the first chair's wheels as well as in front of the table. (00:12:25)
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 Rachel's Going Away Party - S10-E16
Plot hole: In this episode Chandler finds furry black handcuffs, and everybody says that they have never seen them before. How is that possible considering all the people that have moved in and out of that room? How come nobody noticed them when the room and closet were painted green after being pink?
The One Where Monica Gets a Roommate - S1-E1
Revealing mistake: As Monica is walking to her room and steps on Paul's watch, if you look carefully, you can see that she just steps on the band. That would not damage the watch. (00:26:45)
Factual error: The makeup on Rachel's face "can't be covered up with makeup," and "won't come off," we learn in The One In Vegas, Part 2. So it's not a surprise that she still wakes up with it on (and so does Ross.) but an hour or so later, when she's at breakfast, it's not there. An hour or two won't make the magical difference that 8+ hours didn't.
