I couldn’t figure out if you could upload a video, but my Snowy spy cam picked up him staring at the back of his tank and opening and closing his mouth quickly... it looked to all the world like he was barking at his own reflection, but he has not shown any aggression towards his reflection thus far. Is he just being strange? I adore him.
BDs don't have vocal chords, so they can't/don't bark (but they sure can hiss! )
How old is he? Depending on his age, he could be showing aggression toward a reflection.
Is he showing any signs of stress, i.e. stress marks, surfing, etc.?
If he is being aggressive toward his reflection, you can help by attaching wrapping paper or Sunday colored funnies--design inward--to the offending walls of the enclosure. The busy designs will obscure the reflection (and he can read the funnies! :lol: )
FWIW, mine stares at the blank wooden walls of his enclosure (like cats & dogs sometimes do), plants, rocks, basking light, whatever... so he could just be being strange. He stares at us a lot too.