In the episode where Pheobe finds out she is pregant there is a small but obvious mistake. When she answers the phone and the doctor tells her she is pregant she faints, and falls with her head to the right side of the phone, this can not happen, as the phone is sitting to the left of the table. There is no possible explantion of why her head was facing that way, instead of her feet towards the phone. The part where this happens is at the very ending of this episode. Sorry if I am not specific but it is hard to explain!