Continuity mistake: When Rachel and Monica are discussing whether or not Rachel should meet Ross at the airport she's taking a bottle of red wine out of the refrigerator, but when she places it on the table in the next camera shot the bottle of wine is suddenly a bottle of white wine.
Continuity mistake: Rachel tells her neighbor Danny that she doesn't know anything about sailing, but later in the series, Rachel teaches Joey how to sail after he wins a boat at a silent auction. She says she learned sailing from her father while growing up.
Continuity mistake: In the scene where Chandler turns on music when he and Phoebe are going to "have all the sex" you see Phoebe's arm begin to move in the right corner of the screen. When it cuts to her she has not yet begun dancing, and when he goes to turn the music on again it is a duplicate clip from the initial shot.
Continuity mistake: In the scene when Phoebe says goodbye to David, you can see Phoebe's long hair on her back. The scene goes back and forth between Phoebe and David or Phoebe and Joey (after David leaves). Each time the amount of hair on Phoebe's back changes. Sometimes it is a thin bit of hair, other times a large chunk (while the rest of her hair is framing her face in front).
Continuity mistake: The position of the lid of Janice's box of contact paper changes repeatedly and after she tells Chandler she doesn't know what to say, she begins to slide the roll of paper back into the box. In the shot from behind, the box is closed.