The One In Vegas, Part 1 - S5-E23
Visible crew/equipment: After Phoebe tells Chandler that Monica wants to make up and that he needs to find her, when Chandler leaves the room we can see the end of the set wall, with the hallway and another hotel room door, at the left side of the screen.
The One With Rachel's Inadvertent Kiss - S5-E17
Continuity mistake: When Joey is counting the floors of Ross' building (the first time) to find out where Hot Girl lives, he is wearing a black top with a zip. When he rushes over to Ross' building he walks down the hall and knocks on what he believes to be Hot Girl's door. In these shots he is wearing a dark purple button up shirt. As soon as Ross answers the door, Joey is wearing the black top with a zip again. (00:03:15)
The One In Vegas, Part 2 - S5-E24
Visible crew/equipment: At the start of the Netflix version, when the recap scenes from 5x23 Part 1 are being shown, in the shot of Phoebe, Monica, and Chandler on the airplane the end of the cabin set can be seen beside Chandler, at the right side of the screen.
The One In Vegas, Part 1 - S5-E23
Visible crew/equipment: While Phoebe, Monica, and Chandler are with gladiator Joey in the casino, Joey notices the tension between Chandler and Monica, and when he asks what's going on a tape mark can be seen on the floor at the feet of the extra standing at the slot machine, then more tape marks can be seen at the same spot after Monica sarcastically wishes Chandler happy anniversary.
The One In Vegas, Part 1 - S5-E23
Visible crew/equipment: When Phoebe, Monica, and Chandler walk into Caesars Palace Casino, Phoebe notices Joey, and in the next wideshot we can see the camera panning around (it's on a camera crane, presumably filming the overhead angle seen in this scene), at the top right corner of the screen. (Widescreen version).
The One With All The Resolutions - S5-E11
Visible crew/equipment: After his fiasco with the leather pants, powder, and lotion, when Ross is at Monica's and tells the others he's going to kiss Ben goodnight, as he starts walking to the bedroom the camera can be seen at the right side of the screen.
The One With Ross's Sandwich - S5-E9
Continuity mistake: After Joey makes up the story about how he slept with Monica once in London, in the shots facing Phoebe, Rachel, and Ross the door to Monica's apartment goes back and forth being either wide open or closed, depending on the angle of the shot.
The One In Vegas, Part 1 - S5-E23
Continuity mistake: After Joey tells Chandler about his identical hand twin and plans for getting rich, when he sees Chandler's reaction Joey asks, "Are you unsupporting me again?" while he lifts his left arm and points accusingly at Chandler, but next shot it's Joey's right arm that's up and pointing.
The One Where Ross Can't Flirt - S5-E19
Other mistake: While everyone's watching Law and Order for Joey's big scene, Rachel, Phoebe, Monica, and Chandler are sitting on the couch and Ross is standing behind them, but in the TV's closeup the screen reflection reveals an empty couch.
The One Where Everybody Finds Out - S5-E14
Visible crew/equipment: When Ross is using the binoculars to watch Ugly Naked Guy's apartment, the end of the set wall can be seen behind him.
The One Where Everybody Finds Out - S5-E14
Visible crew/equipment: While Phoebe and Rachel are at Ugly Naked Guy's apartment, when Phoebe looks out the window and sees Monica and Chandler the end of the set wall in Monica's apartment can be seen.
The One With The Inappropriate Sister - S5-E10
Visible crew/equipment: When the passerby drops his lit cigarette in Phoebe's charity bucket, the end of the department store facade can be seen at the left side of the screen, and later when Phoebe hands off the bell to her replacement the end of the right side facade can be seen as well.
The One With Chandler's Work Laugh - S5-E12
Continuity mistake: During Ross and Janice's conversation in Central Perk, when Ross comments, "You're ending this with me because I'm too whiny?" both his and Janice's left arms are up, but it cuts to the next shot and it's their right arms which are up, then it happens again when Ross says, "I've become so whiny that I annoy you?! Janice!" they both have their right arms up, but next shot it's their left arms up.
The One Where Ross Moves In - S5-E7
Continuity mistake: When Chandler and Joey walk into the apartment to find boxes all over the place and also when Chandler talks about the air purifier, the door to the bathroom is open and the toilet is right beside the tub (odd that it's there in the first place), but when Joey tells Chandler he wants to play foosball and also when Joey's wearing the helmet, the prop toilet has vanished.
The One With All The Thanksgivings - S5-E8
Continuity mistake: When Phoebe's trying to make the TV work at the beginning, in the close-ups and the first wide shot the remote's at an angle, but in the second wide shot it's straight. It then goes back to being at an angle. (00:00:15)
The One With Ross's Sandwich - S5-E9
Continuity mistake: In Central Perk, when Phoebe writes a note for Ross to put on his sandwich so no one eats it, she mentions that she stabbed a cop, and has a green mug in her hand. It cuts to Monica then back to Phoebe and the mug is out of her hand and she's yelling, "He stabbed me first." When it cuts back to the wide shot the mug is back in Phoebe's hand. (00:05:40)
The One With Rachel's Inadvertent Kiss - S5-E17
Revealing mistake: When Ross is doing his "Watching TV" bit, there is a brief shot of the blank screen that he is sitting on the sofa pretending to watch. In the screen's reflection, it is clear that the sofa is empty. (00:03:55)
The One Where Phoebe Hates PBS - S5-E4
Continuity mistake: Monica comes to get her pan back from Chandler, and when she opens the door, the magna doodle pen is hanging down. The shot changes and it is attached to the board; it changes again and it is hanging once more. (00:12:00)
The One With Ross's Sandwich - S5-E9
Continuity mistake: In the scene where Joey has just brought home his date, he jiggles the door handle, which makes Monica and Chandler run off into Chandler's room. Chandler kicks a circle cushion off the mat, but when the camera cuts back, it's on the mat again, and then off the mat again when Rachel walks in. A red cushion also moves. (00:09:10)
The One With All The Thanksgivings - S5-E8
Continuity mistake: In the scene where they take Chandler to the hospital, Monica hands the bag of ice containing Chandler's toe to the doctor. The doctor is wearing gloves in one shot then no gloves in the next. This goes back and forth three or four times. (00:07:45)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.