The One With The Tiny T-Shirt - S3-E19
Continuity mistake: When Joey and Kate are talking for the first time, Joey is holding a mug. Between shots, sometimes he is holding the mug by the handle and sometimes by the mug, with the handle sticking out. (00:04:40)
The One The Morning After - S3-E16
Continuity mistake: In previous episodes we've seen that from the living room there's a short wall just inside Monica's bedroom (presumably to prevent a clear view inside, as her bedroom set isn't normally there). However in this episode when most of the gang are in her room, they're listening right by the door into the living room with nothing in the way. (00:11:25)
Continuity mistake: Near the end, when Joey is asking Ross if Bonnie's room will be free tonight, he is pointing his hands at Ross. In the very next shot they are in his pockets. (00:20:50)
The One Where No One's Ready - S3-E2
Continuity mistake: The amount of fat in the glass differs throughout the length of the episode. (00:00:05 - 00:15:00)
Continuity mistake: When Phoebe goes to the other Phoebe's house, it's raining, but when Phoebe gets into the house her hair and her clothes are dry. (00:05:00)
The One Without The Ski Trip - S3-E17
Continuity mistake: When Chandler tells Rachel to "shut up; you're not my mom," Joey has both hands on the bottom of the Chinese food carton. In the next shot his right hand is on top of the box. (00:05:30)
The One Where Ross And Rachel Take A Break - S3-E15
Continuity mistake: When Cloe hands Chandler and Joey the flier, it goes from flat to folded to flat in 2 camera cuts with no time to do it. (00:03:15)
The One Where Rachel Quits - S3-E10
Continuity mistake: At the start of the scene in which Ross breaks the little girl's leg, we can see that the stairs are just separated by railings. Later in that scene, when Ross and Chandler start walking up the stairs, there are walls on both sides of them. (00:01:40)
Suggested correction: This isn't completely true. In the first shot, we see railing in the middle, as shown in the screenshot. Then, the shot changes to upstairs, looking down, and we can see the wall, as shown in the bottom picture. However, at the end of the wall, it goes into the railings, which is visible just as the pair start to climb the stairs. A screenshot of this can be seen here: https://ibb.co/bmZ8xTc, making it easier to understand.
The problem with the screenshot is the right side is circled to show there's no railing, but the railing is on the left side (to the character's right), but Chandler is blocking the view of the railing. Ssiscool's screenshot is before Chandler starts to walk up the stairs, which is why it's seen.
The One Where Rachel Quits - S3-E10
Continuity mistake: The gang enters Monica's apartment and it is full of dead Christmas trees. After everybody has entered the apartment we see that the apartment door is shut; the shot then changes to the gang around the sofa, but in the next shot when Rachel answers the phone we can see behind her that the door is open. (00:19:00)
The One With The Hypnosis Tape - S3-E18
Continuity mistake: When Frank Jr is sitting in front of the TV while Davey and Goliath is on, his hand is along the edge of the TV set; however when Phoebe walks in, his arm is straight out. Then when Mrs Knight comes in, his head is straight down and the arm is back along the edge. (00:15:15)
The One With Phoebe's Ex-Partner - S3-E14
Continuity mistake: When Monica comes in and asks Chandler if she can borrow some milk, Chandler is reading a paper that is flat on the bar. In the next shot he is holding it folded, then he lays it on the counter, and suddenly it is in his hands again. (00:14:20)
The One With The Dollhouse - S3-E20
Continuity mistake: When Monica is telling Rachel that guys always say they are going to call, but it doesn't mean they will, she is eating yogurt; in the next shot she has a cup ready to drink out of. (00:14:30)
The One With The Tiny T-Shirt - S3-E19
Continuity mistake: When Mark is telling Rachel they should get back at Ross right there on the couch, Rachel's hands go in a instant from on her chest to down her sides. (00:14:50)
The One With The Metaphorical Tunnel - S3-E4
Continuity mistake: When Rachel and Monica are comforting Chandler, just before he gets up Rachel has her hands on the chair but when Chandler gets up Rachel's hands change position. (00:12:40)
The One The Morning After - S3-E16
Continuity mistake: When Phoebe, Chandler, Monica, and Joey are eating the organic wax, Monica has her feet up on the wall with her legs crossed left over right, but in Joey's closeups when he asks about needing a new walk, Monica's legs are crossed right over left. (00:18:00)
Continuity mistake: When the six friends arrive at the beach house notice the sand between shots. At first it's all wet due to "flood damage", two seconds later the sand's dry. (00:05:30)
The One Where Ross And Rachel Take A Break - S3-E15
Continuity mistake: When Monica and Phoebe are eating with the diplomat and his translator, watch the translator's chocolate cake. It either rotates, has some taken out of it, or is a different piece. Whichever way, the cake changes size, shape or position without him ever touching it. (00:18:10)
The One With The Ultimate Fighting Champion - S3-E24
Continuity mistake: When Robin Williams calls Billy Crystal a b*stard, Monica's purse goes from on her lap to being on her shoulder. (00:01:30)
The One Where Ross And Rachel Take A Break - S3-E15
Continuity mistake: When Rachel is sitting in the window seat talking to Mark on the phone, the glass and the wine bottle move closer to each other. (00:15:50)
The One With All The Jealousy - S3-E12
Continuity mistake: When Ross and Rachel are talking about his playdate with the stripper, a lady in a black vest talks to the people at the table behind them, then goes to the bar and shakes hands with a lady in a black jacket. She does all this again in another shot. (00:19:30)
