Maybe dogs really can talk!
During the day, our dog Mystique is sweet and demure, but at night she becomes a different animal. She guards our house, barking ferociously every time someone comes within earshot. The only problem is that our house is on the main trail where the night staff walk back and forth after dark. Mystique dutifully barks at all passersby whether she has known them for a day or all her life. But if there was really a cause for concern, like a strange man with a gun, I wonder if Mystique would bark in a way that would alert me that there was something dangerous and different about the person approaching the house.
Dog vocalizations may not sound very sophisticated. Raymond Coppinger pointed out that most dog vocalizations consist of barking, and that barking seems to occur indiscriminately. Coppinger reported on a dog whose duty was to guard free-ranging livestock. The dog barked continuously for seven hours, even though no other dogs were within miles. If barking is communicative, dogs would not bark when no one could hear them. It seemed to Coppinger that the dog was simply relieving some inner state of arousal. The arousal model is that dogs do not have much control over their barking. They are not taking into account their audience, and their barks carry little information other than their emotional state.