A dog repeatedly opening and closing its mouth is trying to tell you something, but the cause ranges from harmless to urgent. The most common reasons include nausea, something stuck in the mouth, dental pain, a type of focal seizure, or simply processing an interesting scent. What matters most is the context: how long it lasts, whether your dog seems distressed, and what other symptoms show up alongside it.
Nausea and Stomach Upset
One of the most frequent causes of repetitive mouth movements in dogs is plain nausea. When a dog feels queasy, the body ramps up saliva production, and you’ll see lip smacking, repeated swallowing, and that rhythmic open-close jaw motion as your dog tries to manage the excess drool. This often happens after eating something that didn’t agree with them, during car rides, or when they’re anxious.
If nausea is the cause, you’ll usually notice other signs too: drooling, licking the air or floor, restlessness, grass eating, or eventually vomiting. The mouth movements typically stop once the nausea passes or the dog vomits. A single episode after a meal or car ride is usually nothing to worry about, but repeated episodes over days suggest something deeper is going on with the digestive system.
Something Stuck in the Mouth
Dogs explore the world with their mouths, and sticks, bone fragments, string, or bits of toy can wedge between teeth, across the roof of the mouth, or around the tongue. When this happens, you’ll see your dog opening and closing their jaw, pawing at their face, drooling, and sometimes refusing food. There may be a foul smell from the breath if the object has been stuck long enough to irritate the tissue.
If your dog is calm enough, you can gently open their mouth and look for anything lodged between teeth or pressed against the palate. A stick fragment wedged across the roof of the mouth is a classic culprit. If you can see the object and remove it easily, the behavior should stop almost immediately. If you can’t see anything, or your dog won’t let you look, a vet can do a thorough exam. Some foreign objects sit far enough back in the throat that they’re invisible without sedation.
Dental Pain
Fractured teeth, gum inflammation, tooth root abscesses, and oral tumors all cause dogs to move their mouths in unusual ways. The repetitive opening and closing can be your dog’s attempt to relieve pressure or reposition a painful jaw. Other signs of dental trouble include bad breath, chewing more slowly than usual, dropping food, favoring one side of the mouth, visibly loose teeth, swelling along the muzzle, and pulling away when you touch their face.
Dental pain in dogs is notoriously underdiagnosed because dogs rarely stop eating entirely, even when they’re in significant discomfort. A conscious oral exam at the vet can catch obvious problems, but many dental issues only reveal their full extent under anesthesia with dental X-rays, where vets can probe for deep pockets around teeth and check for damage below the gumline.
Focal Seizures and “Chewing Gum Fits”
If the jaw movement looks involuntary, almost like your dog is chewing gum with nothing in their mouth, it may be a focal seizure. Unlike the full-body convulsions most people picture, focal seizures affect just one part of the brain. The result can be as subtle as repeated jaw clacking, an eyelid twitching, or a lip tremor. Your dog may or may not seem aware of what’s happening during the episode.
A related behavior called “fly biting” or “fly snapping” looks like the dog is seeing and snapping at invisible flies. A study of seven dogs with this behavior found it was most common in Cavalier King Charles Spaniels, Bernese Mountain Dogs and their crosses, Boston Terriers, and Miniature Schnauzers. Episodes lasted anywhere from a few seconds to an hour, and in several cases were triggered by meals or happened at predictable times of day. Some dogs also showed air licking, agitation, hiding, or signs of gastrointestinal trouble like diarrhea and flatulence alongside the fly-biting behavior.
Most focal seizures that only involve jaw movements don’t require treatment. But if the episodes are becoming more frequent, lasting longer, or progressing to full-body seizures, that’s a different situation. Video the behavior on your phone so your vet can see exactly what’s happening.
Canine Distemper
In unvaccinated dogs or puppies, repetitive jaw movements can be a neurological sign of canine distemper. The virus attacks the nervous system and produces involuntary muscle twitching, including a characteristic pattern of jaw chewing and salivation sometimes called “chewing-gum fits.” These neurological signs sometimes appear weeks or even months after the initial illness, and a longer overall course of disease makes neurological involvement more likely.
Distemper is rare in vaccinated dogs, so this is primarily a concern for rescue dogs with unknown vaccine histories, young puppies who haven’t completed their vaccine series, or dogs in shelter environments. If distemper is a possibility, you’d typically see other signs like nasal discharge, coughing, fever, or lethargy either currently or in the recent past.
Jaw Joint Problems
Dogs have temporomandibular joints (TMJ) just like humans, and these joints can dislocate, lock, or develop arthritis. A dog with a TMJ disorder may open and close the mouth repeatedly because the jaw isn’t tracking normally. You might hear a clicking or crunching sound when the jaw moves. In more serious cases, the jaw can lock open, leaving the dog unable to close its mouth or swallow, with the lower jaw visibly shifted to one side.
TMJ problems cause pain when the mouth opens wide, difficulty eating, drooling, weight loss, and muscle wasting along the top of the head over time. If your dog’s jaw seems to be physically limited in how far it opens or closes, or if the lower jaw looks asymmetrical, a joint issue is worth investigating.
The Flehmen Response
Sometimes the explanation is completely benign. Dogs have a specialized scent organ in the roof of their mouth that helps them analyze pheromones and other chemical signals. When they use it, they curl back their upper lip, hold their mouth slightly open, and may chatter their teeth or smack their lips. This is called the flehmen response, and it’s essentially your dog getting a better “read” on an interesting smell.
You’ll typically see this after your dog sniffs another animal’s urine, encounters a new dog, or investigates something particularly fascinating on a walk. It’s brief, voluntary, and your dog looks engaged and curious rather than distressed. No cause for concern.
When the Cause Needs Urgent Attention
Most causes of repetitive mouth opening are not emergencies, but a few combinations of symptoms signal that you should act quickly. If your dog is opening its mouth repeatedly while also breathing rapidly, using its abdominal muscles to push air in and out, extending its head and neck forward, or showing a bluish tinge on the gums, that’s respiratory distress. The dog isn’t just moving its mouth; it’s struggling to get enough oxygen.
Other red flags include a jaw that appears locked open or shut, inability to eat or drink for more than several hours, visible swelling of the face or throat, and repetitive jaw movements that progress into full-body tremors or collapse. If the behavior started suddenly after your dog chewed on something and you suspect a foreign object is lodged deep in the throat, don’t wait to see if it resolves on its own.
For less urgent situations, the single most helpful thing you can do before a vet visit is record video of the behavior. Many of these episodes are intermittent, and your dog may act completely normal in the exam room. A clear video showing the exact jaw movement, how long it lasts, and what your dog does before and after gives your vet far more to work with than a verbal description.