Visible crew/equipment: In the scene where Monica, Joey, and Phoebe are sat on the couch in the coffee house, (whilst the camera is drifting left) a boom mic at the top of the screen is visible for a short period of time. During this time the mic can be seen moving.
Continuity mistake: When Monica and Chandler enter the apartment arguing about what time they were supposed to meet, Monica has her handbag strap over her right shoulder, and then takes it off. When the shot switches to Phoebe claiming to know what time they said they would meet, the handbag strap is back over Monica's right shoulder, and then she takes it off again.
Other mistake: As the wedding begins, the first bridesmaid, Felicity, walks down the aisle with a man. He is not part of the wedding party but is wearing the same attire as the best men. He is not seen again throughout the wedding. The only two men in the wedding party are Joey and Chandler.
Continuity mistake: When Monica is telling Susan and Carol that Ross used to dress up as a girl, Ross goes over to the table and picks up a drink. When he picks it up it has a cork in it. In the next shot he has the cork already in his hand.
Continuity mistake: When Rachel returns from running after the boy that she told to "shut up", you see Joey picking up a piece of food, sniffing it and making a face and then putting it back on the tray. However in the next shot, without moving, Joey is munching on something - he didn't have anything in his hand before.
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.
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.
Continuity mistake: When Joey is reading his speech about all the giving and receiving, Chandler has his legs on the table at the coffee shop. You can see his shoes on the table when they show Joey, but when they change the shot to Chandler his legs are on the floor and crossed.