Answer: Because IT can only get out the way IT went in.
Hexie and Hessian, my two German shepherds, one day suddenly started muzzle grabbing Cousy, my neighbors’ rambunctious and incessantly playful lab. I’ve never seen them do it to each other or to any other dog. In fact, you rarely see dogs do it at all. Why then did they suddenly begin to muzzle grab Cousy, and both of them at about the same time? Roger Abrantes as modern behaviorists are wont to do, has projected a complex human psychology about social status into the minds of canines in order to account for the behavior.
But there is a far more parsimonious answer once we understand the inverse relationship between emotion and stress, the interplay of these two aspects of consciousness being responsible for complex behaviors, such as why one dog might muzzle grab another.
The relationship between emotion and stress is responsible for how an animal learns to direct its force and respond to being the object of force, in kind. Dogs are very astute observers at where other beings “project” their force. In observing humans this means they are quick to deflect their attention onto wherever their owner directs their attention. It’s an eye-to-hand coordination, of the group. So where we direct our force becomes where the dog’s attention becomes drawn. Hence the number one chewed item in the modern household is the TV remote controller. This is completely consistent with how wolves would orient around the one member of their group who is manifesting the most intense fixation on something in their surroundings, i.e. where the prey is to be found.
Between dogs, the direction of force is an eye-to-muzzle coordination and this is the key to understanding the sudden appearance of this behavior in Hexie and Hessian. When Cousy plays with my dogs, she first gets in their face and “knocks” them off balance so that they have to pay attention to her. Then she rolls over on her back and begins to bite their legs and now they can’t stand within jaw range until they finally grab her by the muzzle. At which point she springs up and runs away with them in hot pursuit and reaches her safety zone, the mud puddle at the end of our driveway. So she’s constantly stirring them up, and when they return fire, she flops over and pulls an Inoki versus Mohammed Ali and takes them on from below. They grab her muzzle because this is the source of her force, and this is the same reason a dam would begin muzzle grabbing her pups because their nursing is beginning to hurt.
The operative principle of emotion in equal but inverse relationship to stress is that IT can only get out the way IT went in. This principle can teach us a lot more about the why of animal behavior than the projection of human rationales into the minds of dogs, such as instilling discipline and benevolently enforcing a dominance hierarchy.