Darwin will stop whatever he is doing if he catches a glimpse of his reflection. he runs up to the glass as if it was another dog. Then he'll hunch down and stare, then turn and run, then come back and stare, etc. It is hilarious!
When Luca was younger he used to charge at the mirror and bark at the "other" dog. He never did this with dogs we met elsewhere. My trainer thought it was because he couldn't sniff the other dog. He still gets upset with animals on TV although less so than he used to.
Tori does this when she sees someone out the window at the neighbors house. The person goes inside and she runs to the mirror over my couch on that side of my house and then alas notices herself and barks at the "imposter".... too funny! Silly Doodle!!!