Dogs present themselves differently to other dogs depending on whether they’re protecting their food or goofing around. That’s the conclusion of a new study by scientists at Eötvös Loránd University in Budapest, Hungary. They let dogs choose between photos of two other dogs, while simultaneously playing a recording of either a food or a play growl. (The play growls were made while owners engaged in tug-of-war with their dogs; these animals were not included in the experiment.) One photo was of a dog whose size matched the growl, which reflects the length of a dog’s vocal tract; the other was of a dog either larger or smaller than the growler. When the listening dogs heard the food growl, they focused on the image of a dog who was the size of the growling dog. But when they heard the play growl, they fixed their eyes on the photo of the bigger dog, even though the growl was made by a smaller one, the scientists report in the current Applied Animal Behaviour Science. Dogs give an honest growl when guarding their food, the scientists believe, because a beagle, for instance, might be injured if it decides to play retriever. But a small dog making an “I’m really a BIG dog" growl during play likely knows that the other animal can see its size, and recognizes that it’s essentially making a joke. Dogs likely use the fake growls as they do their other exaggerated play behaviors, the researchers suggest—to reassure each other that the rough and tumble play is, after all, just a game.

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