The reflection stays moving with the rest of the motion in the camera in the original shot, also the reflections eyes stay in motion after the girl
has turned.
Oh I hate that video. As soon as I saw the words 'Japanese girl' in the title I knew what it was but couldn't help clicking!
It scares me but I think it must be some sort of cgi trick, probably an easy one.
Nice and spooky though.
If you are making a movie, then even the none technically minded of us tend to get the target in the centre of the frame, it's not hard, this camera
operator is concentrating too much on the image in the mirror.