The One With All The Rugby - S4-E15
Factual error: Rugby starts with a kickoff and not with a scrum, only the forwards on the team participate in the scrum not the whole team, and there is no scrum half to retrieve the ball from the scrum. The scrum took far too long. There is no structure to the scrum like there should be (props, locks, flankers etc). He doesn't seem to have a team and for some reason everyone just jumps on him, there is no line with one team and another it just seems like a free for all which is nothing like rugby, rugby halves are ended when the ball goes out of play which does not happen here - he just decides to end it for no real reason. Several fouls are committed in the ruck such as coming in from the sides, diving off their feet and holding onto the ball which aren't being penalised. You're not allowed to kick people or harm them intentionally in rugby, there are no cups in rugby but there are mouth guards, which no one is wearing.
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.
Factual error: In season 4 generally, Phoebe has the shortest pregnancy ever. She gets pregnant as the boys win the girls' apartment. In the next episode Ross meets Emily, after 6 weeks he gets engaged to Emily and they then choose to get married 4 weeks later. Phoebe would only be 10-12 weeks pregnant by the time they fly to London, not in her third trimester.
The One With All The Rugby - S4-E15
Factual error: Before Ross goes out to play the second half of the rugby game, Emily gives him some tips on how to hurt the other guys. She singles out one of the guys, saying he doesn't wear a cup. These guys are all English players who love rugby. Rugby players would NEVER wear a cup for rugby is more of a grinding sport than hit and miss. These guys would be crazy to wear a cup.
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 Free Porn - S4-E17
Factual error: We know that Phoebe is three months pregnant, because it's the day after the party where she told Joey that she was three months along. But the ultrasound shows three little lumps that in no way resemble a three-month fetus. An actual three-month fetus is the size of a jellybean.
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.
Suggested correction: It's presented as sarcasm. Not a mistake.
Ssiscool ★
Not clear on where you got that it's presented as sarcasm; nothing in her delivery says so.