Continuity: When Ross confronts Mark, Rachel walks out the back hallway behind her desk. However, after Rachel catches Ross confronting Mark, there's only a wall behind the desk.
Note: The "walls" to the right of and behind Rachel's desk are an L-shaped partition with hall access from either side. Rachel exits to the left of her desk and returns around the partition to the right of her desk. This partition can be seen clearly later this season in "The One with the Dollhouse" when Chandler and Rachel are arguing in the hallway behind the partition and then Chandler emerges to talk to Joanna from the left side of Rachel's desk.