Dogs and humans have developed a special bond during thousands of years of living together. But occasionally our faithful companions do things that leave us wondering, What the heck is that dog thinking? 

Bottom Line Personal asked psychologist and dog expert Stanley Coren, PhD, to explain nine common—and commonly misunderstood—dog behaviors…

Why do dogs walk in circles before lying down? This behavior likely is left over from when dogs slept outside. The leading theory is that walking in circles tramples down long grass, creating a smoother, more comfortable nest. That would explain why pet dogs are most likely to do this when settling down to rest on an uneven or a soft surface, such as a dog bed or carpet. Another theory holds that dogs walk in circles to scan for nearby predators.

Why do dogs kick at the ground after defecating? They’re trying to spread the scent of their leavings over as large an area as possible. For a dog, defecation and urination serve a purpose beyond the elimination of waste—these are ways to mark territory, the equivalent of saying, “I was here,” to any other dogs in the vicinity. Some people believe dogs kick at the ground to cover their feces with dirt, but covering feces is not something a dog would want to do.

Why do otherwise-well-behaved dogs rip up paper products such as toilet paper and tissue boxes? Soft paper ­products feel like fur and feathers in the dog’s mouth, and some dogs find that sensation irresistible. It’s especially common among dogs that originally were bred to catch or carry small furry or feathered creatures, such as sporting hounds and terriers.

Tip: It is very difficult to train a dog to stop ripping up paper products. The best solution is to store oft-targeted items where the dog can’t get at them. You can buy covered toilet paper dispensers, for example.

Why do dogs bury bones (or other toys and treats) and then never retrieve them? If you suspect your dog never goes back to dig up the bones it buries, you’re probably right. The things that dogs bury typically remain buried. The leading theory is that dogs do not remember precisely where they have buried their treasures. Instead, they seem to retain only a fairly general sense of where they tend to bury things. If a dog endures lean times, it will dig in this area and hope to get lucky, but many items will inevitably go unrecovered.

Similar behavior has been observed in squirrels. Some people theorize that squirrels do not remember exactly where they have buried the precious acorns. They know the general vicinity where they have buried them and dig in that area when food is scarce.

Why do dogs chase their tails? Tail chasing is a common form of play for young puppies, but it is rare among dogs older than four months. When a grown dog does chase its tail, there does not seem to be any reason deeper than that the dog suddenly noticed its tail was back there. Typically, tail chasing happens when a dog is in a brightly lit area. The light causes the dog to notice its shadow. While investigating (or chasing) that shadow, the dog suddenly notices its tail, and a brief chase ensues.

Tip: When grown dogs chase their tails, they generally do so for only a few seconds. A grown dog that frequently chases its tail for longer periods is engaging in pathological behavior and likely is in psychological distress. Ask your vet whether medication could treat this problem. The same drugs that help humans cope with obsessive-compulsive disorder can help dogs overcome pathological tail chasing.

Why do dogs eat grass? The current thinking is that dogs eat grass for the same reason that dogs eat anything else—they’re hungry, and it’s the tastiest option available at that moment. Most dogs prefer the tops of new shoots, which have the most flavor.

The conventional wisdom used to be that dogs used grass as an emetic—they ate it when they were feeling ill and wanted to throw up. There is no evidence to support this theory. The high fiber content of grass does sometimes make dogs throw up, but vomiting seems to be less of a dog’s goal when it eats grass than a price it is willing to pay for a snack.

Why do dogs eat their own feces? For its nutrients. Dogs’ intestinal tracts are relatively short, so they cannot always absorb all of the nutrients from food before it is expelled. Eating feces allows them to run food through their systems a second time and absorb nutrients that otherwise would go to waste. That might seem gross to a human, but to a dog, nutrients are nutrients.

Tip: If you want to stop your dog from eating its feces, you may want to switch to a less expensive dog food. Less expensive food usually contains fewer nutrients, which increases the odds that your dog’s digestive system will be able to absorb its nutritional content the first time through.

Why do some dogs bite after wagging their tails? Because wagging does not always mean a dog is friendly and happy. When the tail is held high and the wags are short and quick, the wagging actually is meant as a warning—the dog is trying to tell you to back off. If you approach a dog that is wagging this way, a bite is a possible result. Friendly wags are long and sweeping, with the tail typically held fairly low.

Why do dogs roll in disgusting, smelly things? It’s actually a doggy form of camouflage. When wild dogs hunt, their odor sometimes gives them away—their prey smells the dog approaching and escapes. Rolling in something that has a very pungent odor can mask the smell of the dog.

A second possible reason: Creatures tend to be drawn to things that excite their dominant sense—and smell is a dog’s dominant sense. So perhaps some dogs roll in horrible-smelling things for the same reason that some humans wear brightly colored Hawaiian shirts—it excites their dominant sense…albeit in ways that are difficult for the rest of us to understand.