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.