Other mistake: When Joey comes out the bathroom in the girls' apartment with a turkey stuck on his head, the bathroom floor has the black and white tiles. But that floor wasn't there until Joey put it there in Series 3, The One With Frank Jr. So in the flashback the bathroom floor should be white tiles.
Continuity mistake: When Chandler's boss is slapping all the guys on the butt, on the side of the table closest to the camera there is a tablet with a pen on it. When the guy comes back in to get his briefcase, the pen is no longer there.
Continuity mistake: When Chandler throws his copy of "Chicken Soup for the Soul" under the sofa and it goes across the floor to Monica's feet, she kneels down to pick it up by the counter next to the door, but when she rises, she's next to a chair that's under the table.
Continuity mistake: At the beginning when Rachel falls and starts bleeding, you can see that the wound is somewhere up above her forehead because the blood is running from the wound up there. However, throughout the rest of the episode she has a bandaid going horizontally across her forehead, nowhere near where the apparent wound was.