Dogs do a lot more with their mouths than just eat and drink. Even though they can’t use their mouths to talk, the way they position their lips, jaws and teeth speaks volumes. When your dog is relaxed and happy, he’s likely to have his mouth closed or slightly opened. If his mouth is open, he may be panting-this is how dogs cool their bodies. You might see his teeth because his mouth is slightly opened.A dog who’s frightened or feeling submissive probably has his mouth closed. His lips might be pulled back slightly at the corners. He might flick his tongue in and out, or he might lick if he’s interacting with a person or another animal. When he’s feeling uptight, he might yawn in an exaggerated fashion.
Some dogs show a “submissive grin” when they’re feeling extremely submissive. They pull their lips up vertically and display their front teeth (canines and incisors). This signal is almost always accompanied by an overall submissive body posture, such as a lowered head, yelping or whining, and squinty eyes. Only some dogs “grin” this way. People sometimes mistakenly think a dog is being aggressive when, in fact, he’s grinning submissively and trying to communicate the exact opposite of aggression.
A dog who’s signalling his intention to act aggressively will often retract his lips to expose his teeth. He may pull his lips up vertically to display his front teeth while also wrinkling the top of his muzzle. This is typical of a dog who’s warning you not to come any closer.
A dog may draw his lips back horizontally so that his lips are really tight at the commissure (the corners of the mouth). With this expression, you’re more likely to see both his front and back teeth (premolars and molars). This posture is often indicative of a dog who’s feeling afraid. However, once a dog is ready to bite, he usually pulls his lips up AND back so that his mouth is open and his teeth are exposed.
Dogs can display an “aggressive pucker.” They move their lips forward over their teeth and exhale air so that their lips look puffy and large. You can sometimes even hear them breathing heavily. This display is often accompanied by a wrinkled forehead. A dog who looks like this is saying, “Don’t come any closer.”