“Calvin : There’s no problem so awful, that you can’t add some guilt to it and make it even worse.”
― Bill Watterson, The Complete Calvin and Hobbes
Common Myth: When our pup puts on that doleful, guilty look, they must be guilty of something, right? He/she clearly feels bad for doing something wrong.
TRUTH: Your dog knows you are angry or upset and is using that particular body posture in their attempt of using dog language to get you to calm down and avoid any punishment from you.
The Science-Based Truth Behind That Guilty Expression:
Nearly 75 percent of dog guardians believe that their dogs experience guilt. Just watch Denver Dog, as he is presumed to feel very guilty in this video. It’s a natural tendency for us to interpret animal behavior in our human terms, but when we anthropomorphize (compare animal behavior to human behavior) we can overlook what is really happening. Guilt is a human emotion. Humans often project this guilt onto their animal companions.
Dog guardians observe particular behaviors: “avoiding eye contact, lying down and rolling to the side or onto the back, dropping the tail, wagging low and quickly, holding one’s ears down or head down, moving away from the owner, raising a paw and licking” – and owners believe these behaviors correspond with a dog’s feeling of guilty. However, these are normal and very common dog behaviors that dogs display with each other, depending on the circumstances. These displays are called “appeasement behaviors” – behavior that inhibits or neutralizes aggression in a behavioral partner.
When a dog owner reprimands their dog, especially with loud, deep tones, the dog will attempt to calm the aggressive behavior of the owner (note: aggressive does not necessarily mean violent) with appeasement gestures: lowered head, ears, tail and body and squinty eyes. To the owner, this looks “guilty.”
In reality, the dog is only reacting to the behavior of the owner in the present moment and not associating the owner’s behavior with the actions of the dog that occurred hours before. The owner, however, is gratified by the dog’s appeasement gestures, taking it as evidence that the dog has learned he’s “bad.” ~ 4Paws University

“In wolves, guilt-related behaviors are believed to reinforce social bonds, as in primates, by reducing conflict and eliciting tolerance from other members of the social group. The same could be true of dogs, though their social groups would primarily include humans. Submission serves to keep a social group together, to foster group cohesion.”
The “guilty look” — head cowered, ears back, eyes droopy — is a reaction to the minor (or major) tantrum you are now having over the damage fido did hours earlier. They are not making the connection that you must be upset because of that poop they dropped on the rug, or the shoe they chewed that you left out. They only know you are upset about something, so they are doing what dogs do best to appease each other through nonthreatening body language.
The dog’s guilty look is a response to the owner’s behavior, and not necessarily indicative of any appreciation of its own misdeeds.
A study discovered that the “guilty” look people claim to see in their companion animal is directly related to whether or not the person expected to see the look, regardless of whether or not the dog had actually done something to be “guilty” about. When a dog looks guilty it is because they are reacting to a change in our body language that tells them something is wrong. This leads to a dog’s body language that appears worried or nervous to us. In reality the dog has learned to exhibit these behaviors in order to appease humans who display angry or upset body language. Details of the research studies are here and here.
Unless your dog has been going to canine church behind your back, and has been taught to feel guilty for moral or religious reasons, it’s safe to assume that they are not actually feeling guilty; they are using their canine senses and behavior to carefully appease your anger.
You can learn more about this subject from dog behaviorists, and read their take on it here and here.
Learn more common myths and truths about dog behavior in Decoding Your Dog, a new book from the American College of Veterinary Behaviorists. Drs. Debra Horwitz and John Ciribassi.

Sources:
Scientific American
Discovery
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