Dog communication refers to movements and sounds dogs use to send signals to other dogs and other creatures (usually humans). Dog communication comes in a variety of forms and is part of the foundation of dog social behavior.
Dogs use certain movements of their bodies and body parts and different vocalizations to express their emotions: they move their ears, eyes, eyebrows, mouth, nose, head, tail and entire body, as well as barks, growls, whines and whimpers, and howls.
Dogs lack eyebrows, but some breeds have distinct markings above their eyes.
Dominance and submission
Extensive genetic research has shown that domesticated dogs originated from grey wolves. Wolves primarily live in social family groups called packs in which they exhibit communicative sound and body gestures that can also be seen in their domesticated descendents. Included in this communication are gestures of dominance and submission.
A wolf or dog will show active submission by drawing back his lips and ears and lowering his body. The tail will be low or completely tucked under his body, and its back may partially arch down to further display deference. 
A wolf or dog will communicate a more intense deference through passive submissive gestures. The animal will roll on his back, vulnerably exposing his underside and throat. The paws will be drawn into the body while eye contact is avoided. The tail may be tucked and whimpering noises may be heard. 
- See also: Wolf body language
How high or low the tail is held, in relation to how the dog's breed naturally carries its tail, and how it is moved can signify the dog's mood. When the tail is held high, it shows that the dog is alert and aware; the tail between the legs means that the dog is frightened. If the fur on the tail is also bristled, the dog is saying it is willing to defend itself or pups. If the dog does not have a tail, or it has been shortened or removed via docking, then similar actions may occur with just the hind quarters.
Small, slow wags of the tail say the dog is questioning things around the environment it is in. Either it is not sure whether it should submit, the other creature is friendly, or confused about its surroundings. Large, fast wags of the tail may be a sign of a happy, excited, or an energetic dog, but can also signal aggression.
Dogs are said to exhibit a left-right asymmetry of the tail when interacting with strangers, and will show the opposite, right-left motion with people and dogs they know.
When a dog's lips curl back this shows that the dog has a strong urge to bite. This is an unconscious reflex, designed to get the soft flesh of the lips away from the teeth before the dog bites, and is often misinterpreted as a way of communicating aggressive intent. For example, many dogs will curl their lips back into a "snarl" when they take a cookie or bone.
A rare form of teeth baring is seen in the form as a submissive grin. This means that the dog will be submissive and friendly to the person it is grinning at. In this event the dog will also display other behavioral cues, including tail wagging and lowered posture. The dog sometimes will show a submissive grin when it has recently done something it knows its master would not like, or when it has been caught doing it.
Ear position relates the dog's level of attention, and reaction, to a situation or animal. Erect ears facing forward means the dog is very attentive. They lay their ears back for the sounds surrounding them and also when in a submissive state.
Dogs with drop ears, like Beagles, can't use these signals very well, as the signals first developed in wolves, whose ears are pricked. Wolf-like dogs (such as the Samoyed or Husky) will, when content and happy, often hold their ears in a horizontal position but still forward. This has been referred to as the "wolf smile".
Mouth expressions can provide information about the dog's mood. When a dog wants to be left alone, it might yawn (although yawning also might indicate sleepiness, confusion, or stress) or start licking its mouth without the presence of any food. When a dog is happy or wants to play, it might pant with lips relaxed, covering the teeth and with what sometimes appears to be a happy expression and might appear as a smile to some observers.
Mouth expressions that indicate aggression include the snarl, with lips retracting to expose the teeth, although some dogs also use this during play. However, some dogs will pull back their "top lips" in what looks like an aggressive way, when they are excited or happy. For example a dog prone to "smiling" may do so in greeting to a much loved owner and this should not be punished lest the dog become less affectionate.
A very common form of communication as well, is for a dog to lick another dog, or a person. Dogs lick other dogs' faces and mouths when they greet each other to indicate friendliness. Dogs like to lick human skin not only for the salt from the sweat, but also as a form of greeting, such as by briefly licking a person's hand after sniffing it.
Licking is also used as a social bonding analogous to primate social grooming and stroking. This can indicate intimacy. Such licking is longer and slower, as compared to the brief licking of faces during a greeting.
Eyes and eyebrows
While dogs do not have actual eyebrows, they do have a distinctive ridge above their eyes, and some breeds, like the Labrador Retriever, Rottweiler, Bernese Mountain Dog, German Shepherd, and Doberman have markings there. A dog's eyebrow movements usually express a similar emotion to that of a human's eyebrow movements. Raised eyebrows suggest interest, lowered brows suggest uncertainty or mild anger, and one eyebrow up suggests bewilderment. Eyes narrowed to slits indicate affection for the person or animal the dog is looking at.
Feet and legs
Although a dog's feet lack the dexterity of human hands, a dog can use them as an avenue of communication. A dog might stamp its feet, alternating its left and right front legs, while its back legs are still. This occurs when the dog is excited, wants something, or wants its owner's attention. Pointers tend to tuck one front leg up when they sense game nearby.
This behavior is not communicative so much as the dog exhibiting a fixed-action pattern called "the eye stalk." It is also common for dogs to paw or scratch for objects they desire. Many dogs are trained to mimic a human handshake, offering a paw to a human stooping down and offering their own hand in exchange. Dogs might playfully slap each other with their paws to show gratitude toward one another.
The leaning of a dog's head to the right or to the left often indicates curiosity and/or a sound it has not heard before. It is also used to locate the source of the sound by adjusting the ears, so that sound waves might reach the ears at different times, enabling the source to be located. This, however, may also be a sign of recognition to a familiar word.
If the dog's head is held high with its neck craning forward, it is showing interest, although, it could also mean an aggressive mood if other body language is present.
A bowed head indicates submission and can be a request for physical affection.
- Main article, including bark control training: Bark (utterance)
Dogs bark for many reasons, such as when perceived intruders (humans, dogs, or other animals unknown to them) approach their living space, when hearing an unfamiliar or unidentified noise, when seeing something that the dog doesn't expect to be there, or when playing. Barking also expresses such emotions as loneliness, fear, suspicion, stress, and pleasure. Playful or excited barks are often short and sharp and often made when a dog is attempting to get a person or another dog to play.
Dogs generally try to avoid conflict; their vocalizations are part of what allows other dogs to tune into their emotions, i.e., whether they're aggressive or are in a playful mood.
The bark of a distressed or stressed dog is high pitched, repetitive, and increases its pitch as the dog becomes more upset. For example, a dog that suffers separation anxiety may bark when left home alone.
Some breeds of dogs have been bred to bark when chasing; for example, scent hounds whose handlers use the bark to follow the dog if it has run out of sight. Coonhounds and Bloodhounds are good examples. Such barking is often called "singing" because the sound is longer and more tonal.
Growls can express aggression, a desire to play, or simply that the dog doesn't want to participate in what's about to happen next (being picked up for example). Most pet owners have therefore been urged to treat growls with special attention: always consider the context of a growl and exercise caution. If the threat is very serious, then the dog will usually start off with a very low toned but strong growl that rises in tone if ignored.
Howling may provide long-range communication with other dogs or owners. Howling can be used to locate another pack member, to keep strangers away, or to call the pack for hunting. Some dogs howl when they have separation anxiety.
Whining is a high-pitched vocalization that is often produced nasally with the mouth closed. A dog may whine when it wants something (e.g., food) wants to go outside (possibly to excrete) wants to be let off the leash (possibly to greet another dog or a person) or just wants attention. A very insistent dog may add a bark at the end of a whine, in a whine-bark, whine-bark pattern.
A whimper or a yelp often indicates the dog is in pain or distress and is often emitted by dogs that have been bitten too hard during a play-fight. The whimper or yelp is used only when the dog intends to communicate its distress to a pack member (or human) to whom they are submissive or friendly, and the other dog or human is expected to react positively to the communication; dogs engaged in serious fights do not whimper lest they betray weakness. Dogs also whimper when they are physically abused or neglected by people.
Yelps are often associated with the lowering of the tail between the legs. Yelping can also indicate strong excitement when a dog is lonely and is suddenly met with affection, such as when a dog is left alone in a house during the day and its owner comes through the door late at night. Such yelping is often accompanied by licking, jumping, and barking. Yelping is distinct from barking in that it is softer, higher pitched, and lower volume.
Dogs will often feign injury by yelping to gain the upper hand over other puppies during play. Play yelps are often confused for a sign of pain or distress: the dog not running away after the yelp occurs reveals the ruse.
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- Virtual Pet Behaviorist article on Canine Body Language (ASPCA)
- Virtual Pet Behaviorist article on barking (ASPCA)
- Virtual Pet Behaviorist article on howling (ASPCA)
- International Association of Canine Professionals (IACP)