The One Where Ross Finds Out - S2-E7
Continuity mistake: When Rachel finds out that Ross and Julie are getting a cat, watch Rachel's neck. When she says "together?" she's not wearing a necklace; cut to Ross and Julie for a fraction of a second, then when it cuts back to Rachel saying "both of you?" she's suddenly wearing a necklace. It then disappears again when she says "isn't that just lovely?" hanging off the side of the tray she's holding. (00:05:15)
Big Report - S1-E2
Continuity mistake: Connor (is this cool?) Hammil's shirt is unbuttoned, then buttoned between shots (just as he pushes the woman's head through a pane of glass).
The Puppy Episode (1) - S4-E22
Continuity mistake: In the scene where Ellen goes to Susan's room after Richard makes a pass at her, she has her jacket in her hand when she enters the room. When Ellen leaves the room hurriedly, she leaves without her jacket, but when she is in the hallway about to go back to Richard's room, she has her jacket in her hand.
The Accident - S1-E1
Continuity mistake: In the scene in the kitchen at the beginning of the episode Alex's hair changes multiple times throughout the scene.
The Meeting - S1-E1
Continuity mistake: When Lisa and Ray are talking in Lisa's apartment there is a soda bottle on the table. Part way through the scene a cap appears on the bottle and then is gone in the final shot.
Coach Fussell's Lament - S2-E5
Continuity mistake: Chairface and Chrome Dome arrive at the Brianchild's house in the same car, but drive off in separate cars.