The One Where Paul's The Man - S6-E22
Continuity mistake: When we hear the recording of Chandler answering the phone, it sounds nothing like what Chandler actually said. (00:13:00)
The One Where Paul's The Man - S6-E22
Continuity mistake: When Monica is blaming Phoebe for Chandler hearing the wedding message, Phoebe puts the magazine down on her lap and it's closed, but in the next shot it's open. (00:15:40)
The One Where Paul's The Man - S6-E22
Other mistake: There are two mistakes in the scene where Phoebe spots Joey's picture in the laundromat. For one thing, when Phoebe says "Oh, here it is", she is looking in the opposite direction of the picture. Also, when she says this, her mouth doesn't move at all. (00:16:10)
The One Where Paul's The Man - S6-E22
Continuity mistake: In the opening scene in Central Perk when Paul (Elizabeth's dad) takes Ross to one side to talk to him you can see the girl in the blue top enters the door twice: first the shot after Paul says "I'm funny like that" and then again after Ross says "I realise it upsets you".
The One Where Paul's The Man - S6-E22
Visible crew/equipment: In the scene where Rachel is trying to hide Ross from Paul, when he's about to go into Paul's bedroom after he says "Did you really hear a bear?", look at the window behind Rachel when the shot is on her. You can see a large light reflected in the glass and it moves slightly (not just in conjunction with the camera, it moves before the camera shifts).
The One With The Ring - S6-E23
Continuity mistake: When Rachel is talking to Monica about Paul crying, just before Rachel leaves, Monica has her hair over her left shoulder; the shot cuts and she now has most of her hair over her right shoulder. (00:09:50)
The One With The Ring - S6-E23
Continuity mistake: Paul finally opens up, and cries like a baby to Rachel. While talking to her at the breakfast bar in the kitchen (when Rachel is trying to distract him with sex), he's wearing a white linen shirt that constantly changes between tear-stained and wrinkled to ironed and clean. (00:14:35)
The One With The Ring - S6-E23
Visible crew/equipment: In the opening shot of Phoebe and Chandler in the "nine millionth" jewelry store looking for a ring, at the top of the screen we can see the tip of the boom mic moving in the wideshot. Then, just as Chandler looks into the display case and says, "Ugly ring. Ugly ring. Ugly ring," the boom microphone can be seen moving around in the case mirror's reflection behind him (edited out of HBO Max version).
The One With The Ring - S6-E23
Plot hole: In the opening scene Phoebe and Chandler discuss how Phoebe knows Chandler is going to propose: by walking in on him whilst he was looking at a ring catalogue on the toilet. However, in the previous episode Chandler leaves the apartment right after he found out about Monica booking the wedding slot (on the answerphone) and doesn't come back until he 'freaks out' at Monica and then it is revealed that it was just put on and Phoebe is in on the plan. It doesn't add up, as Chandler would have had to have been looking at the catalogue between hearing the message and deciding to propose, in the same afternoon when he wasn't even in the apartment.
Suggested correction: Chandler decided at some point before the events of TOW Paul's the Man to propose to Monica (and that's when Phoebe walked in). He likely got Phoebe the passes to the museum (because he's the one that said Ross wouldn't be interested). If you look at the episode again, yes, he is freaking out-ish, but this is to fake out the audience. Also, he's "not the groom" because he hadn't proposed yet.
The One With The Proposal, part 1 - S6-E24
Continuity mistake: When they are in Central Perk deciding who will go with Rachel to the auction, Rachel's purse and the cups in front of Joey move around. (00:02:20)
The One With The Proposal, part 1 - S6-E24
Continuity mistake: In the scene where Richard is being seated next to Chandler and Monica, the amount of champagne in Chandler's glass changes. (00:09:20)
The One With The Proposal, part 1 - S6-E24
Visible crew/equipment: After Ross breaks up with Elizabeth, when she throws the water balloons at him and he starts walking away, a crew member's feet are seen standing on a windowsill behind Ross. Additionally, when Ross has exited the building, just as Elizabeth calls to him and he turns around we can see a crewmember, presumably standing beside the second camera, at the bottom left corner of the screen. We know it's not a passerby because he is as tall as the second story window behind him, which means he's elevated on a platform or ladder. (00:19:15)
The One With The Proposal, part 1 - S6-E24
Visible crew/equipment: After Chandler tells Monica about the interesting website and fakes his opinion of marriage, right after Monica says, "Well, that's good to know," in the next wideshot the camera can be seen at the right side of the screen. (00:20:15)
The One With The Proposal, part 1 - S6-E24
Continuity mistake: When the waitress opens the door to the kitchen to tell Monica about a complimentary customer, in the first shot the waitress pulls the door open and stands in front of it, but in the next shot she's pushing the swing door into the kitchen poking her head in to talk to Monica. (00:20:35)
The One With The Proposal, part 1 - S6-E24
Factual error: There's no charity event in the world that would be clamoring for non-paying guests and offering them free food and an open bar.
The One With The Proposal, part 1 - S6-E24
Other mistake: Joey bids on a Catalina 22 yacht, but the picture, and the yacht he and Rachel are on at the end, is a Catalina 18.
The One With The Proposal, part 2 - S6-E25
Audio problem: In the pizza place, after Chandler tells Monica to "put down [her] copy of The Rules..." you hear Monica say, "You know what. I gotta go" when her lips aren't moving. (00:04:26)
The One With The Proposal, part 2 - S6-E25
Continuity mistake: When Monica is in Richard's apartment she gets all worked up, so Richard gives her a hug to calm her down. She goes into the hug with her arms curled up in front of her face, but when the camera angle changes, they are at Richard's back. (00:13:50)
The One With The Proposal, part 2 - S6-E25
Continuity mistake: At the end when Chandler returns to his apartment, from the outside he opens the door with his right hand. Then it cuts to an inside view and he's opening it with his left hand on the handle. (00:17:40)
The One With The Proposal, part 2 - S6-E25
Visible crew/equipment: When Chandler walks in and sees Monica, the boom mic is visible above Monica's head. (00:17:45)