You are scratching your dog behind her ears when she suddenly flips over onto her back, almost grinning with pleasure. Time for a belly rub, she seems to be saying. You may see your dog lying on her back for a number of other reasons, from scratching a hard-to-reach-itch to a defensive move if she's encountered another dog.
Playing with other dogs
One of the ways dogs communicate with other dogs is through body language. A dog lying on his back during play with another dog might be communicating a number of things. It has long been believed that the dog on his back is being submissive and this is his way of telling the other dog that he isn't a threat. However, more recent research suggests there are other meanings to this behavior.
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A 2015 study published in the journal Behavioural Resources conducted by behavioral researcher Kerri Norman and her colleagues at the University of Lethbridge in Alberta, Canada, and University of South Africa in Pretoria, South Africa, concludes that a dog rolling over onto his back is not an act of submission; it is a combat tactic. Of the 248 rollovers during play sessions between two dogs that the group studied, none were submissive. The majority of rollovers were defensive moves to avoid neck bites. The dogs, once on their backs, blocked and launched playful bites at their partner too.
The study also concluded that the act of rolling over during play sessions between two dogs is most often used to facilitate play. An example given is that the larger of two dogs is more likely to rollover than the smaller dog to self-handicap himself and make play more fun, says Scientific American.
Dog and owner play
When you are playing with a dog and giving him attention, he may roll onto his back to tell you he wants a belly rub. You'll know that's what he's after if his tail and legs are relaxed.
But not all dogs like belly rubs. Check for body language. If your dog is relaxed, he's probably enjoying himself, but if his tail is between his legs and he's tense, it's time to stop. If a puppy lying on his back growls during a belly rub, you should walk away, advises K9 Aggression. Pain, illness, or behavior disorders could be the reason a dog growls. Consult your veterinarian if this happens.
Dog sleeping positions
If your dog rolls over on her back and goes to sleep with her legs at a comical outstretched angle or curled toward her body, she is well-socialized and feels relaxed, secure, and comfortable in his surroundings, according to Healthy Pets. A puppy lying on her back also means that she just finds this sleeping position the most comfortable.
This behavior is not common in your dog's wild ancestors because they need to protect their soft underbellies from predators. Your dog's secure indoor bed gives him the confidence to doze off to doggy dreamland in this vulnerable position.