Have you ever caught your dog barking at nothing in the backyard?

I've always caught my sister's Pomeranian barking in the backyard.
I go out there to see what he won't start barking at. I guess he gets irritated with leaves. Every time a leaf flies around he'll bark at it and try to catch it in his mouth. He is only 2.5 pounds, all black except for a white stripe on his chest, & very shy (except to the leaves LOL). He seems to think he's bigger than he actually is. He's get right in Caesar, my Pit Bull's face. Thank goodness, Caesar is very friendly & sweet. He just ignores him. The Pomeranian, Lui has always been really weird. I do believe in ghosts & spirits, and all that...so who knows...maybe he sees something we don't. Like Ram said, perhaps he hears things we don't as well.