Continuity mistake: When Phoebe gives the housewarming gifts to Ross and also when Ross opens the door for the neighbor, his apartment number is "3B" and his neighbor's door is "3A," but in episode 14, "The One Where Everybody Finds Out," the door can be seen three times during the episode, and the number is "201" each time.
Continuity mistake: When Ross tells Chandler and Rachel that he's running out to buy name tags for his party, in the next shot the water bottle beside Rachel does not have its cap on, but it cuts to Rachel's closeup and the cap is on. Other differences can be seen as well, such as Rachel's hair and an extra utensil.
Continuity mistake: After Ross announces his tenure, when Rachel starts crying and tells him that she got fired and didn't get the other job, her right hand is up by her face, but in the next shot her right hand is holding the glass of champagne and it's her left hand up by her face.
Visible crew/equipment: After Monica and Chandler leave the apartment to go "do laundry," Rachel and Joey tell each other that they can't share what they each know, and just as Rachel sits down beside Joey we can see the movement of camera equipment in the window's reflection.
Visible crew/equipment: When the passerby drops his lit cigarette in Phoebe's charity bucket, the end of the department store facade can be seen at the left side of the screen, and later when Phoebe hands off the bell to her replacement the end of the right side facade can be seen as well.
Visible crew/equipment: While everyone's in the apartment Ross is on the balcony talking to Emily on the phone, and in the mirror we can see the reflections of Phoebe and someone else wearing a blue shirt (with a large white pattern) and blue pants (looks like jeans), but none of the others are actually dressed like that.
Visible crew/equipment: While Rachel and Ross are at the apartment, Rachel tries to convince Ross to have brunch with her father so they can get along, and in the shots facing Rachel we can see the movement of a crew member in the window's reflection.
Visible crew/equipment: While Joey's moving into the apartment he gets a little head rush so Monica blames the heat, and just as Monica says that it's the humidity, we can see a crew member with straight light brown hair moving around behind the open door, inside Monica's apartment - and we know it's not Phoebe or Rachel.
Continuity mistake: While Mama Joey is looking for Chick Jr. and Duck Jr., the things pinned to the bulletin board beside the door have vanished when Monica and Chandler walk in, but after Monica walks out to check on the twins everything's back up on the board like it was before.