Continuity mistake: When Chandler kisses Monica before letting the social worker in, she puts her hand on his arm. The camera cuts to her and she says "Tongue, really?" but her hand is by her side now. The camera cuts back to Chandler and both her hands are now out in front of her.
Continuity mistake: In the scene where the gang is watching Joey's "substitution" video, you can easily see the reflection on the television that no one is sitting on the couch, but when the camera goes back to the gang, they're sitting down on the couch.
Continuity mistake: When Phoebe and Rachel are first talking about the apothecary table, there are two piles of CDs on it. In the side shot you can see that the two CDs on the top of the pile in front of Rachel are overhanging by a few centimetres. A few shots later, however, the top two CDs are overhanging on a different side.
Continuity mistake: After Phoebe tells Monica that she is fired from being her wedding planner, Monica says that she has never been fired. However, in "The One with Five Steaks and an Eggplant" Monica gets fired for taking the kickbacks.
Continuity mistake: When Phoebe and Ross are talking about Ross buying his sheets at the flea market, Phoebe says, "Ross, come on, you gotta loosen the purse strings a little" with her hands by her side. The camera cuts and her hands are now out in front of her.
Continuity mistake: When Paul the Wine Guy first comes to Monica's apartment, Phoebe is standing in the kitchen telling Rachel that she just pulled out four eyelashes. But in the very next shot, you can see her sitting in an armchair in the living room. [Broadcast version only - in the extended DVD version there's a shot showing Phoebe walking to the chair.]
Continuity mistake: When Phoebe and Joey are at the coffee house discussing their plan to ruin Ross' blind date just before Joey says, "Ooh I hear that's bad" the pendant on Phoebe's necklace is smooth and blue. When the camera pans to Phoebe after Joey says his line the pendant is flipped over and reveals a new design. This continues to happen throughout the scene.
Continuity mistake: After Joey runs out of the apartment to go make the fake videotape, when it cuts to Rachel walking back into the apartment the table with the tablecloth is quite far away from the front door, but when Caitlin knocks and Ross rushes to go flirt with her that table is near the door.