The basic feature of the canine temperament, the rock-bottom kernel of canine consciousness from which everything about the dog’s nature arises, is that dogs are endowed with an emotional appetite that far outstrips their physical capacity to consummate it. This has many behavioral implications, the most important one being that they are attracted to each other with a force that can’t be consummated by simple social contact and companionship.
Most dogs shake toys only when they play, but shake their toys to display aggression. If the dog is bouncing around in a playful manner or lowering his upper body as he’s shaking, then it’s not a bad thing. However, if the dog is jumping up slightly, raising its head, or shaking a toy over you or a smaller animal, the behavior might be aggressive. This can lead to the dog biting and shaking smaller pets or even young children, so it’s important to stop the aggressive shaking behavior. Work with your veterinarian or an animal behaviorist to create a plan to stop the behavior, which might include removing your attention when he takes an aggressive stance, rewards for proper behavior, and appropriate punishments for aggressive behavior. According to Vetstreet, “Evolutionarily speaking, that motion is how dogs would capture and kill their prey — by grabbing and shaking very hard”.
The consensus points to our dogs’ wolf ancestors and their associated hunting instincts. Although our dogs are domesticated, they still have natural predatory instincts; and since they’re no longer are needed for hunting for food, they come through in the play. They’re apparent in behaviors like pouncing, chasing, tugging, and others – including shaking, and these are all normal behaviors as long as they are playful.
With regard to shaking specifically, we can look to wild dogs and wolves that kill small prey by shaking the animal in order to break its spine quickly and end its life. It’s been said a dog displays this instinctive behavior in much the same way during play: a dog shakes his toy, or his ‘prey,’ to kill it.
Given that calming endorphins are released when a dog chews on toys and also during play and exercise, perhaps toy shaking causes the release of endorphins as well, making our dogs feel good and releasing stress. There’s yet to be a study on it, but it certainly seems to be the case! It is basically a natural and behavioral instinct that dogs tend to have with their toys, according to a discussion on Quora.
Ultimately, dogs end up being attracted to large, dangerous animals or some other type of challenge (these various challenges come through all manner of endeavor, otherwise known of as breed traits) that when overcome does indeed consummate the chronic state of internal pressure that the canine emotional appetite induces. But one of the lesser manifestations of the canine emotional makeup is that dogs can’t just play with a toy, they must make prey on a toy with an intensity commensurate with their constitutional state of frustration and this leads them to shake, rip and tear it into oblivion. Unlike a cat that hunts by instinct, dogs hunt by appetite (emotional hunger), and setting that squeaker free is as close as the dog can get to feeling free when all it has is a fluffy toy to make prey on.
If you enjoyed learning about why dogs shake their toys, you may be interested to figure out why dogs are very hyper after a bath.