Continuity mistake: When Rachel finds out that Ross and Julie are getting a cat, watch Rachel's neck. When she says "together?" she's not wearing a necklace; cut to Ross and Julie for a fraction of a second, then when it cuts back to Rachel saying "both of you?" she's suddenly wearing a necklace. It then disappears again when she says "isn't that just lovely?" hanging off the side of the tray she's holding. (00:05:15)
Visible crew/equipment: At the start, when Chandler and Joey sink into their new Barcaloungers and proceed to recline, the camera can be seen at the right side of the screen. This can also be seen in the show's intro in later episodes. Additionally, set lighting was reflected on the TV screen earlier when Chandler had mentioned "Green Acres."
Visible crew/equipment: Chandler and Joey are spending time with Richard; as they play foosball and Richard scores, he leans back and says "Could that shot BE any prettier?" in a mockery of Chandler. The end of the wall and the hallway behind it are visible (ie the wall set ends). (00:16:00)
Revealing mistake: After Mr. Heckles has been taken away, in the last wideshot while everyone's still standing in the hallway, when this is viewed on the DVD (Warner Bros. S2 set) we can see a long black line on the floor (as noted in another mistake). The problem is that when this is viewed online on Netflix, even though we can see the very same area of floor, that black line has been blurred out. Weird that it wasn't edited on the DVD, and yet it was for the version available on Netflix.
Visible crew/equipment: After the opening credits, just as Joey says that it's unbelievable Phoebe can be married, a camera and yellow electrical cord can be seen at the left side of the screen, and a bit of it is still visible in following shots when Monica mentions the cheeseburger.
Visible crew/equipment: After Chandler throws the basketball and breaks the lamp, in the next shot of Joey as he mentions the bracelet, we can see the reflection of a crewmember (standing behind the foosball table) on the left side of the TV screen (Chandler's reflection is at the center of the screen).
Continuity mistake: When Monica is trying to cheer Joey up, she tells him that she straightened out his shower curtain so it wouldn't get mildew. But in a previous episode (The One Where Eddie Moves In), Joey gives the gang a tour of his new apartment; the shower is clearly visible in the bathroom, and it has a door. (00:18:10)
Factual error: The symptoms (spots, fever, etc) of chicken pox only develop 2 - 3 weeks after exposure to the virus. Therefore, when Ross knew that Ben had chicken pox, Phoebe shouldn't have developed the condition until at least two weeks later, and Ryan certainly shouldn't have developed the disease until the end of his stay (as Phoebe was his only contact with the virus). (00:09:30)
Continuity mistake: The prom video has just ended and the TV screen goes blank. Monica had been sitting next to Rachel, but in the reflection of the TV screen you can see her beginning to stand up. We cut back to a 'real' view, and she's sitting down; then she stands up again. (00:20:25)
Visible crew/equipment: When Phoebe goes to visit her father, there is a little dog outside. Phoebe gets back in the car and the dog jumps up the side of it. When he finally gets part way through the window, the top of the dog-handler's head is visible through the car window. (00:07:00)
Visible crew/equipment: During the prom video, Monica, Rachel, and Monica's date Roy are standing in the living room. When Roy leaves the room saying, "I'm gonna kick Chip's ass," the camera follows him out, but as it's turning the boom mic operator is visible. He's kneeling on the floor sliding the mic toward the girls. (00:20:45)
Visible crew/equipment: After Mr. Heckles is taken away, when it cuts to Phoebe walking out of the kitchen, the reflection of studio lighting array can be seen on the TV screen. Also later in Heckles' apartment, studio lighting's reflected on his TV screen.
Visible crew/equipment: After Monica yells "Stop with the broom, we're not making noise," when both Monica and Rachel stomp their feet the studio lighting can be seen at the top of the screen, over Ross (this doesn't refer to Monica's star light fixture). And when the others join in stomping their feet, we can also see the boom mic dip into view.