Every so often, Thor's reflection comes to life. It's usually when he's looking out at the backyard.
What actually happens is that another black cat comes in and inspects the area. We've seen this cat enough to recognize him: he's a little bigger than Thor and doesn't have Thor's lopsided eyes.
Thor, however, could not be any more freaked out by this if an emissary from the mirror dimension had announced it was here to steal his soul. He stares. His normally slender tail becomes a thornbush. And he starts uttering sounds of distress in some language previously believed extinct among felines.
Unfortunately, I missed my chance to get a picture of their latest confrontation last night. Here Thor is a few minutes after, looking up at me to confirm that he is still himself.