Continuity mistake: Throughout the entire first scene where Rachel is asking Chandler and Monica if they have seen Joey and he's in the bathroom, Chandler is sitting at the table and his blue cup constantly switches from being in his hand to on the table much too quickly to be real movement. At one point he even holds a piece of food which then disappears from his hand back on to the plate.
Continuity mistake: At the end of this episode, Ross enters the door of Joey's apartment and finds Rachel and Joey kissing. Rachel says "I'm so sorry". The next episode, The One When Ross Is Fine, shows the same scene but it has been changed: Rachel never says "I'm so sorry". Joey starts talking when Ross enters the room.
Continuity mistake: At the end of this episode, Ross opens the door of Rachel's room, says "Hi", and then closes it. However, in the next episode (The One With The Jellyfish), this scene is shown again and changed: Ross opens the door of Rachel's room, says "Hi", and doesn't close it - he talks with Rachel and Bonnie with the door open.
Visible crew/equipment: At the very start after Monica says, "We're gonna have lunch at Mom's" when the camera switches to a wider shot look above Joey's head. You can see the boom mic track him across the stage.