And what does "chirp chirp" mean?

When you knock on a door, or ring a doorbell, you may hear a dog barking inside.

THIS IS NOT A SIGN THAT THERE'S A PERSON INSIDE.

This is a sign that there's a dog inside. There may or may not be a human being in there with the dog. Sometimes people leave their dogs behind when they venture out into the world. People often go to their jobs, or to the movies to see Ninja Assassin, or to other people's homes, or wherever else they might like to visit, without their dogs. And the dog doesn't j...