The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: After Phoebe looks down at her belly and scolds the triplets for kicking one another, when Joey walks in and asks if he can borrow a big bowl, studio lighting rigs can be seen at the top right side of the screen.
The One With The Worst Best Man Ever - S4-E22
Other mistake: Given her vegetarianism, and her disdain for fur in another episode, there's no way Phoebe would have wanted a pair of leather pants.
Suggested correction: It's your opinion that Phoebe wouldn't have wanted leather pants, but that's not true of all vegetarians. Natalie Merchant was known for saying she was a vegetarian but still wore leather shoes. I was a vegetarian who would never have worn fur and still wore leather shoes.
The One With The Worst Best Man Ever - S4-E22
Continuity mistake: In the scene where the veterinarian gives the ring back to Ross, there is a dog in the background that goes from standing up to lying down to standing again depending on the shot.
The One With Ross's Wedding, part 1 - S4-E23
Continuity mistake: When Monica, Ross and Emily are going to see the church, Emily's hands move between shots with no time to do so. (00:05:30)
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: In the scene where Phoebe and Rachel are discussing whether she loves Ross, the stage lights are visible in the TV. (00:07:25)
The One With Ross's Wedding, part 1 - S4-E23
Continuity mistake: Rachel is cutting flowers and she and Phoebe are discussing if she loves Ross. Phoebe's necklace switches sides every time the shot goes back to her. (00:07:35)
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: When Rachel gets back from shopping, all the stage lights can be seen in the tv. (00:11:50)
The One With Ross's Wedding, part 1 - S4-E23
Other mistake: When Phoebe tells Rachel that she thinks she can help her get over Ross, she starts by saying that she needs some photos of Ross. Rachel immediately starts walking towards the kitchen, walking right past the red box of photos on the table beside Phoebe (which she will pick up on her way back and then hand to Phoebe), before Phoebe even mentions the chocolate (and then glass of water) she also needs. It's obvious that Rachel is headed for the kitchen before she knows she needs to go there. (00:12:00)
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: When Rachel exits her bedroom and says she's going to London, you can see tape markings on the floor by her bedroom door and the end of the set. Furthermore, you can see a chair which is likely part of the Central Perk set. [Widescreen version]. (00:20:25)
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: At the start of the first exterior shot of the London Marriott Hotel, when the camera pans to the left and reaches the awning the reflection of the camera/crane can be seen, and we also see it turn and lower.
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: After Ross and Monica talk about Emily's dream of the perfect wedding and perfect guy (and Monica's pillowcase), when it cuts to Phoebe and Rachel at the apartment we can see a crew member (wearing a blue shirt) at the left side of the screen, before Phoebe mentions that she thought of a good flaw. (DVD).
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: When Joey, wearing the Union Jack hat, walks into the hotel room while Chandler's sitting on the bed, on the widescreen version we can see the end of the set wall at the right side of the screen. On the DVD, just as Joey walks across the room studio lighting can be seen at the top left side of the screen.
The One With Ross's Wedding, part 1 - S4-E23
Visible crew/equipment: When Rachel opens the door to the apartment while she's holding flowers and sees Phoebe trying to get up from the couch (before the wedgie comment), the open edge of the set wall can be seen at the top left corner of the screen.
The One With Ross's Wedding, part 1 - S4-E23
Plot hole: The wedding is threatened because Ross, Emily, and Monica discover that the location has been torn down a few days early. However, when one plans an event, especially a wedding, one puts down a deposit to hold the location, signs a contract, and has all of that in writing. The church would not have allowed the tear-down to happen early as they'd be in breach of contract for accepting money and then allowing the church to be torn down before the wedding. And if they had broken the contract, Monica would have been screaming about it and demanding a refund.
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: In the scene where Monica and Ross discuss how Emily has decided to call off the wedding after Monica suggests they postpone the wedding, Monica is wearing a black watch on her left wrist. This disappears and re-appears a number of times throughout the scene. (00:15:00)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: In the episode where Rachel goes to tell Ross she loves him (in England) she leaves her room with a brown sleeveless vest and a cardigan over her shoulders. The cardigan then disappears in all other shots until after Phoebe says "he's in love with the British chippy". Her leather jacket also goes from being in her hands to over her arm. (00:19:30)
The One With Ross's Wedding, part 2 - S4-E24
Audio problem: When the wedding officiant says "take thee, Ross" his lips don't move. (00:20:35)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: When Phoebe is on the phone to Emily's mum she is making a sandwich. We see her put mayonnaise on it, the shot flicks to Emily's mum then comes back to Phoebe and the mayonnaise is now gone. (00:26:45)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: When Felicity finds Joey outside the wedding venue she closes the door. But when they start kissing, the door is completely open. (00:35:50)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: As Ross says, "This is our wedding day," in a close-up, Elliott Gould is holding a bit of paper in his left hand (glasses in his other hand, out of shot). In the wide shot, the paper is in his right hand, then jumps back to his left when the angle changes. (00:36:25)