Continuity mistake: After the pool incident when David is writing letters. Monica is looking over the letters that David has written. There's a point where you can see that she's still holding at least 2-3 sheets of paper but when the camera shifts back to the writing there's only one in her hand. There should be more than one paper in her hand. And when viewed from behind her back the sheets are neatly lying on top of each other, when seen from the front, the sheets are tilted.