Factual error: When Ross shows Chandler the book, he claims it is in "the biggest library on campus" at NYU, which would be Bobst library on Washington Square Park South. Later, in Central Perk, when Ross tells Rachel and Joey about the people "making babies" in front of his book, Joey says, "Wait a minute. Fifth floor, against that back wall?" Bobst's fifth floor is conference rooms only; there are no stacks on that floor. Joey might have been confused, but Ross should know better, being a professor and having just visited that location. (00:08:30)
Revealing mistake: When Ben sits on the sofa to listen to Ross talk about the festival of lights, you can see Monica move Ben to the other side of the sofa despite there being space for her to sit. This is so they sit in the correct order as she would mask Ben to the cameras.Max Thompson
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.
Audio problem: Chandler, Monica and her parents are at dinner to discuss the upcoming wedding. When they describe how they remodeled the kitchen when she broke up with Richard, the camera pans to Monica and her mouth is moving but there's no sound. It then switches camera angles and Monica audibly asks, "Well what about when I started dating Chandler?" Which is what she said in the frame before with no sound. (00:11:00)
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)
Continuity mistake: When Ross and Monica are at the wedding reception talking to the other guests at their table, a lady wearing a red scarf is standing behind them with her back turned. Throughout the scene the red scarf keeps changing position very quickly - in one shot it's slid down one shoulder, then back up in the next and then slid down again. At the end of the scene it's off her back entirely and she has just slung it over her arms. (00:12:15 - 00:13:15)Babatomyfriends