The One Where They're Up All Night - S7-E12
Plot hole: It is made clear through dialogue in the episode that Joey and Ross are stuck on the roof because Joey removed the bit of piping holding the door open. However, when Tag, Rachel and Phoebe get up to leave, Phoebe says "Shh, get me out of here" and there is a clear shot of the door standing wide open. Afterward, it is possible to see Tag reaching for the door handle to close it behind him. This is inconsistent with the idea that the door needs to be held open. (00:02:20)
The One Where They're Up All Night - S7-E12
Revealing mistake: Just after Ross realises that he and Joey are locked out on the roof, he goes over to the door and tries the handle with some force. That whole part of the set moves - door and walls. (00:03:25)
The One Where They're Up All Night - S7-E12
Revealing mistake: When Chandler is getting a pan out to warm some milk, he successfully pulls the bottom pan out without too much disruption, however, the joke (and entire plot device - to wake Monica up) is to make as much noise as possible so Perry pulls out more pans on purpose and knocks them on the floor. This is quite clear - you can see him grasp the wok and pull it out onto the floor. (00:06:30)
The One Where They're Up All Night - S7-E12
Continuity mistake: There is a long shot of Rachel and another person sitting on the sofa and Rachel's wine glass is almost empty. She then goes over to the the counter to fill it up. However, before she starts to fill it, a significant quantity of wine can be seen in the glass. (00:07:35)
The One Where They're Up All Night - S7-E12
Factual error: In the opening scene, Ross remarks on the stars the group is gazing at. In reality, there would be far too much light pollution in this part of New York City to be able to see any celestial bodies such as comets or stars.
The One Where They're Up All Night - S7-E12
Visible crew/equipment: Right after Tag wonders if he can see his apartment from there, when Ross says "wow, look at all the stars" a boom-mic is visible for a short amount of time.
The One Where Rosita Dies - S7-E13
Continuity mistake: In this episode we seemingly understand why Ross and Monica's parents favor Ross. In one scene at Monica's apartment Ross says that it is because their parents thought Judy was barren. This would make sense except that in TOW Rachel's Book, Jack and Judy tell Monica and Chandler that they had to get married because Judy was pregnant. Judy was using a diaphragm as birth control and Jack's dog ate it. It doesn't make sense that Judy would use a diaphragm if she thought she was barren. This was not news to Monica since she said she had heard the story about the dog eating her mother's diaphragm at her 5th grade Halloween party. (00:04:15)
The One Where Rosita Dies - S7-E13
Continuity mistake: When Chandler and Rachel figure out that the chairs were switched they both head over to Joey's apartment. When they enter the apartment, the new black chair can be seen with tags attached to the top and left side. When the scene cuts to Joey sitting down the tags are all missing from the chair. (00:20:05)
The One Where Rosita Dies - S7-E13
Visible crew/equipment: When Joey sits on the Lazy Boy chair Rachel purchases, there are a pair of denim jeans seen behind him - the crew member steps back out of frame but can still be seen.
The One Where They All Turn Thirty - S7-E14
Continuity mistake: As Monica is giving her speech while drunk, at one point her hands go from her sides to gripping each other between shots. (00:00:10)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In one of Monica's flashbacks, her hands move between shots with no time to do so. (00:10:50)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In the shot of Tag giving Rachel a scooter, her shirt is fine. The next shot of Rachel, she has a bow from the present on her shirt. The next shot is of Chandler, then next shot of Rachel the bow is gone again. (00:11:55 - 00:12:25)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: When Monica is at the party and she is drunk, there is one point when she is sitting down on a chair with Chandler on her right. Chandler is holding her left hand (which has a snack in it), but when it cuts to a front view of Monica, suddenly both her hands are on her lap. (00:13:45)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: Rachel's birthday has always been in May, not February/March. (00:16:00)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: Rachel is said to be the youngest in the group as they reminisce about their 30th birthdays, however this episode reveals that almost all of the characters ages have been inconsistent throughout the series. In Season 1, Joey is said to be 25. In Season 2, he says he is 28. In S7 E1, he says he is 31. In Season 1, Monica is said to be 26. In Season 7, she should therefore be at least 32. Rachel graduated high school with Monica, so she should also be about 32 in S7, not just turning 30. She would have been 26 in S1. But, in Season 4, she refers to herself as a "28-year-old cheerleader". Based on Season 1, Joey should actually be the youngest member of the group, not Rachel.
The One Where They All Turn Thirty - S7-E14
Plot hole: There's no way Phoebe has lived to 31 without knowing her birth date. She's had "real" jobs (like the massage parlor) and those require social security numbers and accurate birth dates. She didn't go to high school, but she mentions classmates, so she must have gone to elementary/middle school, and those required birth dates even in the '70s and '80s. She's also "lived in Prague," which she couldn't have visited without a passport - which requires a birth certificate.
The One Where They All Turn Thirty - S7-E14
Continuity mistake: In The One Where They All Turn Thirty, it is Rachel's birthday. They show flashbacks of all the other Friends' thirtieth birthdays despite Monica's birthday supposedly being months after Rachel's. Plus, earlier on in the show Joey was 25 when Monica was 26, and since Monica and Rachel were in the same grade Joey should actually be a year younger than them, not a year older.
The One With Joey's New Brain - S7-E15
Character mistake: After Susan Sarandon slaps Joey the first time, after he tells her that her character is dying on DOOL, she turns away and right before she is off camera she smiles, instead of maintaining her anger. (00:06:05)
The One With Joey's New Brain - S7-E15
Continuity mistake: When Joey is talking to the woman whose brain he receives, as the shot changes she is holding a glass, then a cigarette then a glass again, with no time to change objects, let alone anywhere to put the other. (00:06:05)
The One With Joey's New Brain - S7-E15
Visible crew/equipment: When Monica and Chandler are going over to the window to see Ross playing the bagpipes, the head of a crew member is visible on the left side of the screen, standing by the framed poster. (00:07:30)
Answer: Usually by the seventh night of Hanukkah you don't know what to get the other person, and you will probably resort to getting the other person something insignificant. Chandler is basically saying that the pen is a stupid gift.