When Jason is cutting Marie's hair in the hotel room, his watch is on his left wrist. When he and Marie begin to kiss, in this flipped shot Jason's watch is on his right wrist, his moles have changed sides, and the hand-held showerhead behind them is backwards as well. Next shot his watch is back on his left wrist. The flipped shot has nothing to do with the small bathroom mirror.
In the beginning, after Jason gets off the train, there is a shot of Jason outside at night looking up a snow-covered street with some footprints in the snow leading away from him. These footprints belong to director Doug Liman.