My dog barks at her own reflection in the mirror and also on our glass sliding door. At night, the door is basically a huge mirror, and I have to pull the curtains closed, or she will bark at herself. I have also found that when the light hits the mirror a certain way, it triggers her to bark. My solution has been to cover the window and move the mirror where she cannot see it. She does not do this as much now, but reflections were a big trigger for her when she was younger. Now, as she is getting older (she’s 14), I think her reflection truly startles her at times. It looks like another dog but has no scent, so I can understand why this might be confusing to her.