Revealing mistake: In the episode where Joey is doubling Al Pacino's butt you can clearly see his shadow when he's shooting the scene in the shower, and he's wearing boxer shorts. (00:13:20)
The One with the Blackout - S1-E7
Revealing mistake: When Chandler is choking on the gum, you can see it is still in the left side of his mouth in a huge lump. (00:16:45)
The One with the Blackout - S1-E7
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: After Chandler asks the woman out, he runs back over to the group shouting, "She said yes! She said yes!" As he does this Joey can be seen mouthing the line. (00:03:45)
The One with Two Parts: Part 1 - S1-E16
Revealing mistake: If you look closely you can see that the name of the restaurant "Riff's" is printed on by computer in post-production. (00:00:05)
The One Where Underdog Gets Away - S1-E9
Revealing mistake: Whenever Monica's apartment is shot from the point of view of the balcony looking in, fake walls have to be put up across the room to cover the open space (since there is no wall there usually). When the friends are looking out the window at Ugly Naked Guy and his girlfriend in this episode, you can see that the rear wall does not extend nearly far enough - there is a large black space behind Monica. (00:19:25)
The One with Two Parts: Part 2 - S1-E17
Revealing mistake: In the scene where Phoebe goes to see Ursula at Riff's, Ursula goes to get Phoebe her birthday present. When she sits down, you can easily tell, by looking at all the people there, that the shot has been sped up. (00:15:10)
The One with the Dozen Lasagnas - S1-E12
Revealing mistake: After Phoebe tells Rachel that Paolo made a pass at her, we see a shot of the outside of Monica's apartment block and Rachel is throwing Paolo's clothes out of the window. Look closely and you can see the clothes have been very badly superimposed on to the background. (00:17:05)
Suggested correction: The show sent a crew to New York to film the clothes being thrown from the same building that is used in establishing shots. In a wide-screen version of the episode, the clothes can be seen being thrown out a window (although in the episode the clothes are supposedly thrown off a balcony).
The One with the Blackout - S1-E7
Revealing mistake: When Phoebe says something like, "Look, the last candle is about to go out", she starts counting down, saying "-47,-48..." and you can see Monica looking at the candle. But there is a light source behind her (it can't be a candle because she is looking at the last candle). (00:20:05)
The One with All the Poker - S1-E18
Revealing mistake: When Rachel is doing the shuffling trick, it is clear that it is a trick deck. The cards, whilst flying from one hand to the other, change the angle of flight in mid-air, and some of them even move backwards as she moves her hands further apart from each other. This could only happen if the cards were connected to each other. (00:13:20)
The One with the Fake Monica - S1-E21
Revealing mistake: In the scene when Marcel has to get on the plane. It is obvious that David Schwimmer is just shaking his leg and Marcel is doing nothing besides sit on David's foot. It is especially obvious in the second shot. (00:20:45)
The One with the Dozen Lasagnas - S1-E12
Revealing mistake: When Rachel throws Paulo's clothes over the balcony, they land on the corner of the building, yet the balcony isn't near the corner as there are bedrooms between the place where she throws them and the edge of the building. (00:17:15)
The One Where Monica Gets a Roommate - S1-E1
Revealing mistake: As Monica is walking to her room and steps on Paul's watch, if you look carefully, you can see that she just steps on the band. That would not damage the watch. (00:26:45)
The One with the East German Laundry Detergent - S1-E5
Revealing mistake: When Ross and Rachel are looking at the pink clothes in the washer, it's clear the clothes are actually dry. (00:17:20)
The One with the Candy Hearts - S1-E14
Revealing mistake: When Chandler bangs his head on the bathroom wall after realising Janice is at the restaurant, the wall wobbles, revealing it is part of the set. (00:04:15)
The One with the Candy Hearts - S1-E14
Revealing mistake: When Rachel pours the rest of Palo's stuff in the fire, it's clear she pours it on the table not the fire. However, the flames billow up. (00:13:40)
Revealing mistake: When Joey is filming his scene for the movie, look behind the director to see a box saying 'Monica' indicating that it was shot on the Friends set rather than Al Pacino's set. (00:16:30)
The One with Two Parts: Part 2 - S1-E17
Revealing mistake: When the scene cuts from the apartment to Riff's, a man on the other side of the street walks past the Riff's sign and the sign is still visible through him, revealing it is just animated.
The One with Mrs. Bing - S1-E11
Revealing mistake: When Chandler finds out Ross kissed his mom, he leaves and slams the door behind him. After he slams the door, the wall wobbles slightly, revealing it's part of the set. (00:15:05)
The One with the Ick Factor - S1-E22
Revealing mistake: In the scene where they are in the coffee shop talking about Rachel's dream about Chandler. Rachel is carrying a coffee pot around then sits down. When she sits she puts her hand under the coffee pot, which would be extremely hot if it were real.
