The One With Rachel's Crush - S4-E13
Other mistake: Monica supposedly single-handedly changed over the guys' apartment from carpet to polished hardwood in two days. There's no way that someone of her size could have moved all that furniture solo (Rachel didn't help since she's totally surprised), stripped off all the carpet, sanded the wood, stained the wood, let it dry, and then replaced all the furniture, in two days.
The One With The Dirty Girl - S4-E6
Other mistake: When Rachel tells Joey he can't get Kathy another "coupon for an hour of Joey love", you can see Chandler (Matthew Perry) mouthing the words "Joey love". (00:17:21)
The One With The Fake Party - S4-E16
Factual error: Phoebe says in the show that she's three months pregnant. Not only is she way too big for that, but the fetus also kicks for the first time. Women don't feel fetal movement until 16 weeks at the earliest, and for a first pregnancy it may not be until 25 weeks or so.
Suggested correction: Phoebe's size could partially be explained in that she was carrying triplets, though Lisa Kudrow was pregnant in real life, and was further along than her character. Her pregnancy had to be written into the show and the gestation timelines did not match up. Phoebe feeling "movement" could just be her imagination, as her character is supposedly somewhat psychic and often perceives things that are not necessarily discernible to others or isn't even real.
Continuity mistake: When Chandler's partner says she's going to be late for Andrew she has her hands in front of her. Camera changes and now one hand is up by her hair. (00:18:15)
The One With The Giant Poking Device - S3-E8
Factual error: The "very long poking device" that the friends fashion out of chopsticks would never actually work. It has vulnerable points every half-foot or so (the length of the chopsticks) and after a certain point would just break or sag under its own weight at one of the vulnerable points.
The One With Ross's Teeth - S6-E8
Character mistake: While on his date with Hillary, Ross says that he has a five year old son. Ben was born in 1995 and this episode is set in 1999, so Ben should be four, not five.
The One With Joey's New Girlfriend - S4-E5
Continuity mistake: When Ross goes to Amanda's house for a date you see her two children sitting on the couch. The little boy with blonde hair is sitting down, when it cuts to Ross and Amanda talking the boy is standing up on the couch, the next shot he's sat down as Amanda walks out the door.
The One With The Screamer - S3-E22
Factual error: Rachel's date yells at the theater patrons who are in the gang's seats; one of them has D13, and he screams "you're surrounded by even numbers, does that give you some clue?" However, the establishing shot shows they're at the Lucille Lortel Theater, which has odd-numbered seats on the left - the side they're sitting on. It is also a relatively small house and doesn't have a D13; the outermost seat in that row is D9. (00:04:50 - 00:05:30)
The One with the Monkey - S1-E10
Visible crew/equipment: When Chandler is demanding someone to kiss him, a boom mic can be seen slightly dropping into the shot. (00:24:20)
The One Where Underdog Gets Away - S1-E9
Continuity mistake: When the six are looking out the window at Ugly Naked Guy cooking his turkey, they are looking straight across the alley into his window. In "TOW The Giant Poking Device", Ugly Naked Guy's apartment is several floors below theirs in the adjoining building.
The One With The Ballroom Dancing - S4-E4
Visible crew/equipment: When Phoebe and Rick are sat on the massage table, keep an eye behind Phoebe's head when the camera is on her, particularly after Rick says, "I can always find another masseuse." You can see the shadow of the boom mic moving.
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank is trying to melt a spoon there's one shot where he holds the spoon high above the table, then the angle changes and he's pressing the spoon against the plate.
The One With Phoebe's Uterus - S4-E11
Continuity mistake: In the scene where Joey is showing kids around the museum, there's a little boy who corrects Joey about the existence of the Mastodon. The kid's arm is by his side at the beginning of the scene. When he begins saying, "Isn't the Mastodon from the Pliocene Epoch?" his left arm is suddenly up and his thumb pointing at the Mastodon. (00:07:05)
The One Where Ross And Rachel Take A Break - S3-E15
Continuity mistake: When Phoebe rushes in at the start she has a coat on. Camera cuts to Monica then back to Phoebe, and the coat is off. There is not enough time to take it off. (00:00:15)
The One With The Fertility Test - S9-E21
Visible crew/equipment: When Chandler is given the cup at the clinic, a boom shadow can be seen on the wall. (00:12:50)
The One With All The Cheesecakes - S7-E11
Continuity mistake: In the scene when Phoebe says goodbye to David, you can see Phoebe's long hair on her back. The scene goes back and forth between Phoebe and David or Phoebe and Joey (after David leaves). Each time the amount of hair on Phoebe's back changes. Sometimes it is a thin bit of hair, other times a large chunk (while the rest of her hair is framing her face in front). (00:19:10)
The One With Ross and Monica's Cousin - S7-E19
Continuity mistake: When Cassie shows Ross her freckles on her shoulder, her hand positioning changes between shots.
The One With Ross's Tan - S10-E3
Continuity mistake: Chandler walks away from Ross's apartment at the end. But he walks to where the kitchen should be. (00:21:15)
The One With The Princess Leia Fantasy - S3-E1
Continuity mistake: S3E1; Ross is telling Chandler about how woman tell each other everything in Central perk. Chandler puts a book about trout on the table and then talks to Ross, then the camera zooms out and the book has moved more to his left and a coffee mug is in front of it.
The One Where Ross Hugs Rachel - S6-E2
Audio problem: In the pre-theme-song scene, with Phoebe and Ross talking outside the coffeehouse, when Phoebe sends Rachel away in the cab for the second time the sound of the tyres screeching starts while the cab is still stationary.
