My Reflection Can See Something I Can't

I walk into my hallway and to find a music box sitting on the floor. I pick it up, and start playing there was no twirling figure in the box just the mirror reflecting my face, I stared at the reflection that was didn't look back at me it looked behind me, then so did I, there was nothing. Absolutely nothing expect for the hallway. My reflection hasn't ever looked in my eyes since only ever staring behind me and can't help but wonder what is it looking at?