It took me several minutes too, but to get to a different conclusion: I didn't notice the lack of reflection you mention, what I noticed is that the real Arnie

It took me several minutes too, but to get to a different conclusion: I didn't notice the lack of reflection you mention, what I noticed is that the real Arnie must be the one "inside" the mirror, while the one giving us its back is a fake. This way they could open the port-cover in the head in a single shot!