Hippy is right. Everything is backwards in a mirror. For example, my face looks fantastic as a reflection, but I know that I ACTUALLY look like my face got smashed by a train. It's like some kind of cruel black magic.
Vision is the reflection coming off the object we are looking at, reflections like in a Mirror. The brain knows this, and flips it so we see it the right way. So when we look in the mirror the brain doesn't know the object has already been flipped, so it flips the object as it always does, trying to correct it, in doing so it turns it backwards again. this is hard to imagine, but think about it.