Brad

The One With Ross's Denial - S6-E3

Corrected entry: In the scene where Rachel asks Phoebe if she can live with her Phoebe claims to have a roommate called Denise. However in a previous episode 'The one in Vegas part 1' Rachel and Phoebe are talking about walking around the apartment naked and Rachel says "you live on your own" to which Phoebe agrees saying "Yeah, why do you think it takes me so long to answer the door".

The One Where Underdog Gets Away - S1-E9

Corrected entry: In this episode, when Chandler is telling Rachel his Thanksgiving story, he says that he had just had a mouthful of pumpkin pie when his parents told him they were getting divorced. However, in 'The One With All The Thanksgivings', in the flashback, Chandler is eating turkey when they tell him (hence the houseboy saying 'more turkey Mr. Chandler?').

duncanmc

Show generally

Corrected entry: Matthew Perry was so famous for missing his mark while taping that he developed the backward slide that you see him do in almost every show. He would come bounding into his scene slide backwards looking down for his mark and then hit it. (Per the tour guide at Warner Brothers Studio).

Boobra

The One In Vegas, Part 1 - S5-E23

Corrected entry: When Phoebe is looking at herself in the mirror with Joey's gladiator hat and says that she should start wearing hats, the microphone's reflection is visible at the top of the mirror.

The One With Rachel's Going Away Party - S10-E16

Corrected entry: When packing up the spare room in Monica and Chandler's apartment, the boys find a pair of fluffy handcuffs in the wardrobe. Monica and Chandler painted the room and inside the wardrobe when Rachel moved out; wouldn't they have found them then?