There is dim lighting by and behind the camera and / or the camera angle is such that reflections from the mirror do not point to the camera. These are my best two hypotheseses.

There are a few methods, which you can easily deduce yourself with a mirror, a pal, and a camera of any kind: A) the camera is positioned at an angle (off to the side) to the mirror's reflection, thus being out of the frame that includes the subject; B) the camera is hidden behind a one-way substance like a gauze, a treated glass, a hidden opening in, say, a bookcase behind the subject, etc. Examples of this are when you see hidden camera footage taken from a hat-cam -- the lens can be behind the special gauze or surface that allows seeing out but not in. It can also be hidden in the wall behind the subject, even when you can't see it in the edited version. These are only two of several, but I've witnessed these and not the others (digital touch-up, treated mirror glass, etc.)

Heres how we did it on the film Irreversi shot in Hong Kong. You can see in the reflection behind the actor that he is looking into a mirror. we start the shot by showing the actor and then pull the zoom to show the mirror. image is copyright 2008, Bigfoot Films, All rights reserved.

There are different ways to keep the camera out of a mirror shot: The easiest is to just line up the shot so that the camera (and all other movie "stuff") isn't being reflected. Or, if your shot HAS TO line up more directly with the mirror, you'd have to do one of two methods... the first is to cover the "mirror" with green or blue and then "comp" the color out and replace it with whatever shot you need reflected. Obviously more planning and work is involved. You can see an example of this in the movie CONTACT when the girl runs upstairs and opens the bathroom vanity. The other option is to create a second "mirrored" room through the frame that only looks like a mirror. You can see an excellent example of this on the TERMINATOR 2 DVD extras. It is a scene that was filmed but not used in the movie. I once had to shoot an interview with a gymnast in a room with mirrors on every wall. It became a lesson in geometry as there was precisely one angle I could point the camera without seeing my camera and the lights. This was an example of number one above which I found was a huge challenge to pull off. Brian Dzyak Cameraman/Author IATSE Local 600, SOC http://www.whatireallywanttodo.com