You should also consider what your dog considers. They can hear and smell things you can't, while they always try to consider what you pay attention to. Intetspecies teamwork makes the dream work :3
I did that once, the cats were staring out the window with wide-open eyes, so I joined in to see what the hubbub was all about... and there was a silver fox on the porch, staring back at us.
There we all stood, all frozen in place for a while, like some sort of "Mexican standoff".