When Monica asks Rachel if she has ever taken the rubbish out, she has the milk carton in her hand. When the camera pans back, she has the rubbish bag in her hand, with no time for her to have gotten it.
When Chandler and Ross approach the desk at the gym, the attendant is putting a clipboard on the desk. After Chandler tells him he wants to quit the gym, the camera angle changes to behind Chandler and the attendant is once again putting the clip board on the desk.
Right before Treeger comes to get Joey to rehearse one last time, the gang is in Monica's apartment, and daylight is coming in through the windows. When Treeger and Joey go up to the rooftop, which is only moments later, it's suddenly nighttime.
Joey tells Rachel and Monica that they owe him big time, when in fact they don't because Joey was the one who created and instigated this problem to begin with. Response: The problem had many sources including Rachel, Monica and Treeger.
In the opening scene, the whole reason Rachel has to go to the trash room is because Monica has accused her of putting an empty pizza box back in the refrigerator. Moments later in the trash room, when Rachel is confronted by Mr. Treeger, she opens the pizza box and offers him the two slices of pizza still in the box.
Monica tells Rachel the trash room is the third door on the left, and later, Monica heads to the trash room herself, turning right as she leaves the apartment. The only thing to the right is the stairwell.
Phoebe mentions that she's never been fired before. But she was fired from her singing job at Central Perk.