Interesting! In this case, was it used to avoid showing the camera?
Surely it's intended as a more deliberate (not technical) device - seeing his 'reflection' we're seeing him as he sees himself, his self-image. (I haven't seen the film though.)
Oh, I understand the cinematic effect, what I'm asking is why they used a trick instead of an actual mirror. I suppose because the actual mirror would have shown the camera behind, right?
You are correct!
Without using this technique you'd have the camera in shot.
I don't think it would work with an actual mirror - either Cassel will block the mirror or the camera will block Cassel.
Very cool! I didn't know that. It's amazing all the kinds of shots that are done in movies that one would assume are trivial to accomplish, but that actually require tricks.