The One With The Football - S3-E9
Other mistake: The accent of the Dutch woman is not a Dutch accent at all. It appears to be Scandinavian. (00:07:00)
Starring: Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matthew Perry, David Schwimmer, Matt LeBlanc
The One With The Football - S3-E9
Other mistake: The accent of the Dutch woman is not a Dutch accent at all. It appears to be Scandinavian. (00:07:00)

The One With The Apothecary Table - S6-E11
Visible crew/equipment: After Ross and Rachel cover the table with the sheet, when Phoebe walks in Rachel says they can turn out the lights and watch the movie, and in the next shot we can see the end of the set wall, the soundstage and a crew member's leg.
Trivia: The Magna-doodle on the door in the boys apartment has a different picture on it every episode. There is usually some tenuous connection between the picture and the plot of the episode.
The One With The Jellyfish - S4-E1
Question: When Ross and Rachel are fighting, Chandler hides behind the door and bursts out saying, "I knew it!" When Rachel says, "It's not that common, it doesn't happen to every guy, and it is a big deal!" is this just a Chandler moment or is there another joke I have missed?
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom