The images we see in the mirror are the pure incarnations of evil. They are only allowed to exist in the area reflected in the glass. To them, life is like a never ending hell, rotting away in the same room day after day. The only release from this purgatory is death, and the only way for them to die, sad to say, is if YOU die.
Fortunately, they are bound by a code. You are their master, and they must mirror your every movement and expression. To do otherwise would break an unbreakable law, unraveling the space-time continuum. However, there is a loophole, and it can only be triggered by you, the master. To force them into error is to free them from their contract; after you let them out of your view, you're on your own. Know this: when you watch them, they're watching you back. They're watching. And they're thinking.
The next time you're alone in your room, turn down the lights. Think of something on your body that varies in length, such as hair. It must be clearly viewable from your perspective. Grab a ruler and, looking in the mirror, quickly grab a hair at random; you must confuse it. Hold it in position as best you can and note the length. Look down. Yours will be different.
Don't look back up.
Don't turn your back to that mirror ever again.