The One with Two Parts: Part 2 - S1-E17
Corrected entry: When Monica is filling out Rachel's medical information, she has to change the name on the form so Rachel can use her insurance. You can see that she has a pencil in her hand. However, she goes up to the desk to get a new form. It makes no sense that she would arouse suspicion when all she had to do was erase Rachel's name and put hers.
The One Where the Monkey Gets Away - S1-E19
Corrected entry: In TOW Rachel loses the monkey, she calls animal control. Ross comes home and is shouting at her when the woman comes. Rachel asks who it is, but never actually buzzes her in, yet somehow she gets in.
Correction: Good timing explains this one. If anyone was coming out, or a resident with a key was going in they could simply hold the door for her.
The One with the East German Laundry Detergent - S1-E5
Corrected entry: In this episode, when Monica and Joey are at the restaurant and Monica is talking to the other girl in the bathroom, the latter says that Bob is "really great in bed," to which Monica states that Ross didn't even tell her when he lost his virginity. However, in the previous episode when Ross remembers that it's the anniversary of he and Carol...consummating their physical relationship, he says he told EVERYBODY (including Monica).
Correction: He may have told her that they'd slept together, but she didn't know it was his first time - she probably assumed it was important just because it was Carol.
The One Where Monica Gets a Roommate - S1-E1
Corrected entry: In the very first episode where Rachel turns up after running away from her wedding, Ross hits her with an umbrella. But only a second later he is sitting with a coffee in his hand.
The One with George Stephanopoulos - S1-E4
Corrected entry: In the episode in series 1 where all the girls are having a sleep-over at Monica's, they're all lazing around and the camera shows Monica laying on a sofa, picking at a large bowl of cookie dough with a wooden spoon. While she is speaking, you can clearly see her accidentally flick a piece of cookie dough out of the bowl onto the floor. If this was the 'real' Monica, I'm sure she would have freaked out and cleaned it up straight away.
Correction: The girls had been drinking, so it's possible that Monica was a little too buzzed to care about it, or even notice it in the first place.
I can't recall any episode where Monica drops her neat and tidy persona. Her O.C.D. always controls her. I think the cookie dough is a mistake in the show that they let go or didn't see.
The One Where Nana Dies Twice - S1-E8
Corrected entry: When Monica is reading about the cheap casket, in the shot from behind her there is obviously a sticky-note that has been placed in the brochure.
The One with the Monkey - S1-E10
Corrected entry: Early in the scene when Ross is introducing them to Marcel, look over Chandler's shoulder - a person is visible going into a bedroom.
Correction: This is wrong, it's Phoebe going into the room (check the clothes) after she's been speaking with the gang, she walks off.
Correction: Insurance forms often have multiple carbon copies. Even a pencil will leave a carbon impression on the other pages from the pressure of the tip. If there were no carbons used, the pencil point still leaves an impression on the top copy, even when erased. Monica is also perfectionist, she did not want there to be any revealing inconsistencies on the form.