Revealing mistake: In the scene in the coffee house, Phoebe is talking to Monica who is drinking a cup of coffee. Towards the end of the scene, the camera is on Phoebe who is smiling & laughing at Monica. In the right hand corner is a side view of 'Monica' however, it is not Courtney Cox in the scene, but a completely different actress. [Widescreen version only, although the "wrong" nose is visible in the original]. (00:06:20)
Revealing mistake: After Mr. Heckles has been taken away, in the last wideshot while everyone's still standing in the hallway, when this is viewed on the DVD (Warner Bros. S2 set) we can see a long black line on the floor (as noted in another mistake). The problem is that when this is viewed online on Netflix, even though we can see the very same area of floor, that black line has been blurred out. Weird that it wasn't edited on the DVD, and yet it was for the version available on Netflix.
Revealing mistake: While Monica and Rachel are talking about Chandler's "jollies to Jaws" Rachel's wearing a colorful flowery top, and after Joey walks in just as Monica takes her seat at the table in the closeup, it's Jennifer Aniston's stand-in, wearing a blue top, who is seated beside Monica. And Rachel's hair is waivy in the flowered top, but straight in the blue top. (Viewed in widescreen).
Revealing mistake: In the scene when they confront the stripper at Chandler's office. Ross starts shouting about his grandmother's ring, and as Chandler says "way to be cool, man", you can see Joey ducking behind Ross, covering his mouth with laughter. A brief cut away, then back and he's standing with the others again looking serious. Widescreen version only.
Revealing mistake: When Phoebe and Mike walk into Central Perk and announce they're moving in together, Chandler, Monica, and Ross, who's wearing a sweatshirt and khakis, are all sitting on the couch, and after Phoebe's comment about loading up the Volvo and wanting to be a soccer mom, it's David Schwimmer's stand-in, wearing a blue button-down shirt and jeans, who is seated beside Chandler.
Revealing mistake: When Rachel tells Joey that his agent called and he got the audition for the Broadway play, Rachel's wearing a colorful paisley top, and after Monica says, "Maybe the monkey will be at the audition," in the next shot it's Jennifer Aniston's stand-in, wearing a red plaid blouse, who is standing beside Joey. (Widescreen).
Revealing mistake: At the point in the ceremony where Joey forgets the rings, the camera pans out and you see Chandler step sidewards to get the ring from Ross, and Monica step sidewards to get the ring from Rachel and Phoebe. As Monica moves, her dress slides across and one of her feet is revealed; it has what looks like a brown boot or heavy brown shoe on it. (00:44:20)
Revealing mistake: When Rachel first meets Paolo she's looking for the cat in candlelight, holding the candle in front of her. You can see her shadow on the wall, as well as the shadow of the candle, revealing that the light is not coming from the candle. (00:07:25 - 00:14:30)
Revealing mistake: On a number of occasions in this and the next episode, the beach and the water can be seen in the background, through hotel windows. White foam is visible in a number of places, like the crests of waves, but not only do they not move while the camera is on them, they are always in the same place in subsequent shots, revealing that this is a painted backdrop. (00:26:40)