Continuity mistake: At the beginning of the movie, Leonard looks outside his window and sees room 304 (which will be given later to him on top of his current room) - it is on the same floor he is currently on. Still, when he learns from the clerk that he has been ripped off, we see them both coming out of room 21, which probably is room 221 with the first 2 missing, because it's next to the reception, itself located on the second floor (we know that because from room 304, Leonard only needs to go down one flight of stairs to reach it). Both his rooms, 304 and 221, could not possibly have been on the same floor. (00:06:40 - 00:26:25)