Is there hidden meaning in your dog's growls? In the April issue of Animal Behaviour, scientists report on an experiment in which they put a pooch in a room with a juicy bone. As the animal approaches the bone, the researchers play a recording of a dog growling to guard food from an interloper. In most cases, that stops the dog in its tracks. However, if the researchers instead play a recording of a dog growling at a stranger—which sounds very similar to the human ear—the experimental dog is usually not deterred from the bone. The researchers say this may show that dog growls are not generic hostile warnings, but actually convey content. Whether animals can communicate this way is a hot topic in animal cognition circles. Some monkeys can specify the type of prey they've spotted through their alarm calls. But this type of ability in dogs hasn't been proved.