What Do Dogs Dream About?

So my dog woke me up early this morning, barking and insisting that he needed to leave the bedroom. I got up, opened the bedroom door, and followed after as he zoomed down the hallway, down the stairs, and into the living room. There, he checked out the back of the house and the front of the house before deciding that he had chased away the Bad Guys.

(Obviously I praised him for being a Good Boy and protecting the house.)

But as I lay back down, I wondered what woke him up. Was he dreaming about chasing something when a sound woke him up? I know that he dreams, because he falls asleep on me on a regular basis and then dreams.

But what do dogs dream about? Squirrels? Cats? Chipmunks?

Oh, my.

What do you think?