Your reflection does. It's you. That's how it is with mirrors.
Why are you afraid? When you turn your back, your reflection turns hers, unnoticed. Refelctions do what the real person does, in front of the mirror. That's what they do. If you talk, does your reflection not talk, at the same time? yes. If that happened with a real person, there'd be no conversation.
There's nothing to fear. If you think your reflection is alive, some how, you think too much about the two personality blonde gal in Heroes. Of course, her problem was sort of explained in chapter 10 or sooner. Here's what you should do. Force yourself to stand in front of a mirror. Relax, and do different things, such as move your arms like a clown, hold your pet upside down. Bend over as if to pick up something, back turned. Looking under yourself at the mirror, what do you see? Your relfelection in the same position. Now with a camcorder recording and aimed at the mirror, stand up with your back, to the mirror. Next do some other things in front of the mirror. When done, watch the video. What do you see your reflection doing? Now, ask yourself- 1. Whose that? 2. How is it she did exactly what I did? What's the answer? I know it, do you, sweetie?