Keep double mirrors and you can check your butt. Why tire your neck?This is normal stuff. I doubt he never did that. Even during the MM shoot? That's absolutely unbelievable for me at least, after all he is a celeb.
If an actor says 'I have a mole on my face and I have never seen it', people here would be very upset if somebody comments that's unbelievable... They would say 'Do you have special powers to see your face? Nobody can see their own faces you know, only other people's faces'.
619