Continuity mistake: In the bar, Cathy is trying to set Chandler up with one of her friends. When the camera is facing Chandler, we see Cathy's hand rubbing Joey's back, but when it cuts to a front shot of Joey and Cathy, her arm is down in front of her. Then without having had enough time to move, her elbow is up on the table and she is holding hands with Joey.
Continuity mistake: At the beginning of the episode where they are watching Ross through the window, Phoebe is leaning forward and standing to the left of the pole next to Chandler. When the shot changes to Ross coming through the door, she is suddenly standing up straight and is now behind Joey and Chandler.
Other mistake: When Phoebe accidentally allows Chandler's ring to be sold, she tells him that she overheard which restaurant the guy said he was taking his girlfriend to, so they can go find him and persuade him to exchange rings. However, in the previous scene we see that Phoebe was paying no attention at all to that guy - she was too busy trying on jewellery. She wasn't even within earshot of the guy, and we see from her reaction that she hadn't even noticed him at all before he left the store with the ring (during which time he doesn't say anything at all).