The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: Joey is in their hotel room asking Chandler where Monica is, and the open bathroom door behind Chandler alternates from wide open to halfway open between shots.
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 The Free Porn - S4-E17
Continuity mistake: When Joey is asking Ross why he told Emily that he loves her, Joey's bottle of juice is right in front of him. In the next shot of Joey, there's two bottles - Monica's Diet Snapple and Joey's juice, and in the next shot it's back to one again. Monica's drink appears and disappears throughout the scene. (00:11:25)
The One With The 'Cuffs - S4-E3
Continuity mistake: Joey's encounter with the encyclopedia salesman is riddled with errors. First, when the salesman is talking about Van Gogh and saying "He painted that," he points to a page that is all text; later, Joey is reading about vomit, and it is at a pont much further on in the book than when the salesman read about vulcanized rubber (which it shouldn't be, given the encyclopedia is alphabetized); finally, when Joey buys the "V" volume, as he opens it he has a $50 bill in his hand, and when the shot changes to show the salesman he is somehow folding and pocketing it without having taken it from Joey. (00:13:00)
The One Where They're Going To PARTY! - S4-E9
Continuity mistake: When Chandler answers the phone and it's Gandalf calling to cancel, Ross is just opening the fridge, but the shot cuts to Chandler with the phone and Ross is putting two beers down on the side next to him - too quick to have got them there from the fridge. (00:05:35)
The One With Rachel's Crush - S4-E13
Visible crew/equipment: When Rachel comes in at the start of the episode a stage light is reflected in the TV. (00:02:05)
The One With The Ballroom Dancing - S4-E4
Other mistake: In the scene where Rachel is going to take out the trash, Monica tells her the garbage room is the 3rd door on the left. However, when Rachel comes back with the pizza box and Monica leaves for the garbage room, she leaves the apartment and walks towards the right - there are no doors that way, just the stairs. (00:00:50)
The One With Chandler In A Box - S4-E8
Continuity mistake: In the scene were Phoebe is calling for Monica's eye doctor, in the background you can see the TV is off. Then Phoebe asks if she wants to see the on call doctor, Monica says yes, and in the background the TV is on. (00:03:55)
The One With Ross's Wedding, part 2 - S4-E24
Other mistake: In the episode with Ross's wedding to Emily, Joey is talking on a cell phone with Phoebe as he walks down the aisle. Joey holds the phone out to Ross saying 'it's Phoebe', and one can clearly see that the phone's screen is completely blank. The phone isn't even turned on. (00:39:20)
The One With Phoebe's Uterus - S4-E11
Continuity mistake: When Monica is drawing the seven erotic zones, she says there are seven and Rachel says, "Let me see that!" Rachel has one leg on the couch and then in a flash she has them both on the table. (00:14:05)
The One With All The Rugby - S4-E15
Continuity mistake: When Rachel is talking to Joey about flushing the toilet, her hands go from counter to bottle top to counter with no time between camera cuts. (00:02:00)
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 The Dirty Girl - S4-E6
Visible crew/equipment: When Monica leaves the kitchen into the next scene, the boom mic is visible at the top of the screen above the kitchen door for a short period of time. (00:07:40)
The One With The 'Cuffs - S4-E3
Continuity mistake: In Joanna's office, Chandler and Rachel are pulling his pants from one another while he is cuffed to the filing cabinet. Right before Rachel says "What if I clean your bathroom for a month?" she throws the pants onto a chair, but then when Chandler later says "Freedom. I want my freedom. Why won't you hear me?" he opens the door to yell to Sophie and they are both holding the pants again. (00:15:10)
The One With Phoebe's Uterus - S4-E11
Continuity mistake: At the beginning, Alice and Frank tell Phoebe that they have been trying to get pregnant. When Alice says, "You know, no one's getting any younger", Frank looks at Alice and laughs. In the next shot however, he is looking at Phoebe and doesn't seem to laugh. (00:01:00)
The One With The Worst Best Man Ever - S4-E22
Visible crew/equipment: After Phoebe gets very annoyed by the leather pants gift, when she stands up and walks to the bathroom the boom mic can be seen at the top of the screen, just as she pulls the crepe streamer down.
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 Chandler In A Box - S4-E8
Visible crew/equipment: When Monica and Tim are on the balcony, we can see the end of the set wall, as well as studio equipment and lighting, at the left side of the screen.
The One With The Fake Party - S4-E16
Continuity mistake: When Rachel is talking to Joshua near the drinks table at the party, he is holding a blue cup in his left hand and nothing in his right (this is most obvious when she's offering him a cherry). When she begins to choke, he raises his empty right hand to pat her on the back, then when she walks away there is suddenly a bottle in his raised hand. The shot changes, and his hand is again empty and he reaches down to the table and picks up the same bottle. (00:08:30)
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.
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom