what is kismet doing?

Kismet is normally pretty quiet. But sometimes he sees something in the back yard for front yard that catches his attention and he just won't shut up about it. He posted up right there in front of the back door and barked and barked. I grabbed his leash and took him out to see what it was he was popping off about, but he just went out and looked around and came back in. What a freakshow.