I'm watching this Nova special, and it's fantastic. I'm completely amazed. As a dog owner, I already knew that Roo could tell my emotions and that I could pick out what her specific sounds mean. But to see it backed up with scientific studies is awesome.

They have a group of people that they let individually listen to several different barks, and these people could identify anger, anxiousness, playfulness, etc in the barks.

If you have a chance (it's on Netflix Instant Play), find Dogs: Decoded and watch it.