The One With the Sharks - S9-E4
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. Rachel's hair is wavy in the flowered top, but straight in the blue top (viewed in widescreen). (00:12:22)
The One With The Boob Job - S9-E16
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.
The One With The Mugging - S9-E15
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). (00:03:08)
The One Where No One Proposes - S9-E1
Revealing mistake: While everyone's looking at Emma through the window, when Jack makes the comment about the first grandchild, someone in the background walks by and causes the hallway's set wall to wobble behind them.
The One In Barbados, part 1 - S9-E23
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)
The One In Barbados, part 2 - S9-E24
Revealing mistake: When Ross is talking to the weird obsessive scientist at the bar, just before the wife comes in, the wall behind the professor moves in shot to allow the cameraman room to swing around in the next shot. (00:40:20)
The One With The Soap Opera Party - S9-E20
Revealing mistake: When on the roof for the party, the view of the city is obviously fake. (00:12:20)
The One With Rachel's Other Sister - S9-E8
Revealing mistake: When Chandler grabs his bag he accidentally lets the box full of wedding china fall off the stool. Watch closely (play in slow-motion). The box falls on the floor and shattered china falls out. The china was ALREADY broken before it falls on the ground. (00:23:00)
The One Where Emma Cries - S9-E2
Revealing mistake: When Emma starts crying and Rachel picks her up, look at how much the baby is moving when she takes it out of the cot. In the next shot it's suddenly only moving it's head, and very slowly at that. This is because it's a robot - and it's very obvious. (00:06:10)
The One Where No One Proposes - S9-E1
Revealing mistake: When the nurse hands Emma to Rachel, you can tell it's not a real baby. (00:08:10)
The One Where No One Proposes - S9-E1
Revealing mistake: When Rachel is breastfeeding Emma for the first time, the baby's head is constantly moving in the same repetitive pattern suggesting it is one of those life-like dolls. Babies do not move their heads like that. (00:08:20)
The One Where Monica Sings - S9-E13
Revealing mistake: When Joey has his eyebrows plucked at the salon, it is obvious that the woman is not pulling any hair off. (00:07:00)