In an obedience class for adolescent dogs, Denny, a male Rottweiler, and Meadow, a female Doberman, investigate one another. Denny circles Meadow and tries to mount her from behind for the third time in a row. This proves too much for her. In an instant, Meadow’s lips retract as her body becomes tight, and before we know it, Denny is on the ground with Meadow standing over him, growling. Meadow continues to stand over Denny, whose ears curve back and eyes narrow. When Denny licks and paws at her open mouth, Meadow’s demeanor softens. She steps away and, facing him, folds into a deep play bow. They dance away from us like big, romping puppies as we release a collectively held breath.

I could tell by the alarm on some of the human participants’ faces that they had feared the interaction would end badly. However, Denny and Meadow were not strangers to one another. They had played together regularly in a previous puppy class, but this was the first time they had interacted in a way that raised questions about exactly what they were up to. Were they fighting? Should we have allowed their interaction to play out, or does anything that looks like aggression between dogs immediately call for intervention?

Because we live with multiple dogs, study dog behavior and work professionally with aggressive dogs, we think a lot about canine aggression. Some dog interactions clearly qualify as aggressive — for example, a dog with a history of initiating unprovoked attacks and inflicting damaging bites is clearly aggressive, and letting her interact with other dogs is dangerous. No one would disagree about this. However, what about cases where teeth are f lashing, spit is flying and the growling is deafening, but in the end, neither dog is the worse for wear? This is a gray area that is so very interesting precisely because it’s often not clear-cut. Are these instances of aggression?

The answer depends upon whom you ask. Even among behavioral scientists, the term “aggression” can have so many meanings that, in effect, it has lost its meaning. For example, behaviorists might use the word “aggressive” not only to describe a dog who has killed another dog but also to describe a dog who growls or snarls at a dog who is trying to take his bone. The motivations and emotions are clearly very different in these two examples. In the first case, the dog intended to do harm and did, but in the second case, the dog was likely just communicating his displeasure. Using the same word to describe two completely different scenarios can affect how we think about and respond to a wide variety of dog-dog interactions.

Perhaps a more useful term to describe growling at a potential bone thief or the interaction between Denny and Meadow is “agonistic behavior.” Ethologists, who often use this term when studying nonhuman animals, define agonistic behaviors as those that occur between individuals of a particular species in conf lict situations. Examples of agonistic behaviors in dogs include threats like muzzle-puckering and growling; submissive behaviors like crouching, lowering the head and tucking the tail; offensive behaviors like lunging and snapping; defensive behaviors like retracting the commissure (lips) while showing the teeth; and attacking behaviors like biting. With the exception of biting that results in punctures or tears, none of these behaviors necessarily indicates intent to do harm. They simply reveal emotion (e.g., anger or fear), communicate intention (e.g., to maintain control of a resource or to avoid an interaction) or function as a normal part of play fighting (e.g., growling, snapping or inhibited biting). To determine if an interaction meets the criteria for “agonistic behavior,” an observer must focus on an objective description of the communicative patterns displayed rather than automatically jumping to judgments associated with the use of the term “aggression.”