When a horse shows its teeth, it can mean several different things depending on the context. Horses expose their teeth for reasons ranging from processing an interesting smell to expressing pain, signaling submission, or even responding to trained cues. The key is reading the rest of the horse’s body language alongside the teeth display to figure out what’s actually going on.
The Flehmen Response: Analyzing a Smell
The most common and most misunderstood reason a horse shows its teeth is the Flehmen response. The horse extends its neck, raises its nose, opens its mouth slightly, and curls back its upper lip, fully exposing the front teeth. It looks bizarre, almost like laughing, but the horse is actually doing something sophisticated: routing an interesting scent to a specialized organ in its nasal cavity.
Horses have an accessory olfactory system called the vomeronasal organ that detects pheromones and other volatile chemicals. When the horse curls its lip during the Flehmen response, the organ expands and contracts, pulling the scent in and sending chemical information directly to the brain. Stallions do this frequently around mares, especially during breeding season, but all horses display the behavior when they encounter a strong or unusual odor. A new feed, a strange animal’s scent, or even an unfamiliar cleaning product can trigger it. If the horse’s neck is stretched upward and the upper lip is dramatically curled, you’re almost certainly looking at a Flehmen response, and the horse is simply gathering information.
Aggression and Warning Signs
Teeth baring with a very different posture signals aggression. An aggressive horse pulls its lips back to expose both upper and lower teeth, often with ears pinned flat against the head and the neck extended forward toward the target. This is a clear threat, and it frequently precedes biting. You’ll see this during resource guarding (over food, water, or space), in dominance disputes between horses, or when a horse is telling another animal or person to back off.
The distinction from the Flehmen response is straightforward. An aggressive horse’s body is tense and directed at the perceived threat. The ears are back, the eyes may show white, and the overall posture is confrontational. A horse performing the Flehmen response, by contrast, typically has its head tipped upward and isn’t focused on any particular target.
Pain, Colic, and Gastric Ulcers
Horses in physical distress often show their teeth in ways that look different from both aggression and the Flehmen response. Lip curling and teeth grinding are recognized signs of colic, which is a general term for abdominal pain. Gastric ulcers, one of the most common conditions that mimics colic, produce similar outward signs because the damaged stomach lining causes persistent discomfort.
Researchers have developed the Horse Grimace Scale to identify pain through facial markers. A horse in pain typically shows a combination of signs: ears held stiffly backward, tightening around the eyes, tension above the eye area, visibly strained chewing muscles, and a strained mouth with a pronounced chin. The mouth and jaw tension is particularly telling. Unlike the relaxed, upward lip curl of the Flehmen response, a pain-related teeth display involves tightness through the whole face. The jaw may clench, the lips pull back in a strained way, and the horse may grind its teeth audibly. If you notice teeth showing alongside any combination of these facial tension markers, especially with other behavioral changes like pawing, rolling, or reduced appetite, the horse is likely in pain.
Foal “Snapping” as Submission
Young horses have their own distinctive teeth display called snapping or champing. A foal rapidly opens and closes its mouth, exposing its teeth in a clacking motion, often directed at an older horse. This behavior serves as both a submission signal and an expression of high emotional excitement. Foals frequently direct snapping toward stallions, essentially communicating “I’m not a threat” during social encounters. The behavior is normal and typically fades as the horse matures and develops more adult social signals.
Yawning, Stress, and Frustration
Frequent yawning is another way horses end up showing their teeth, and it’s worth paying attention to. While an occasional yawn is normal, research has found that horses kept in stressful conditions, particularly social isolation in stalls with restricted feeding schedules, yawn significantly more than horses in lower-stress environments. Horses displaying repetitive stress behaviors like cribbing or weaving also yawn more frequently, and both behaviors tend to spike during the same time periods, especially when horses go long stretches without access to forage.
Frustration appears to be the common trigger. In one study, horses that received no hay in the afternoon showed more yawning and more stress behaviors during those hours compared to the morning when hay was available. If your horse yawns excessively and shows other signs of restlessness, it may point to management changes that could help, like more turnout time, social contact with other horses, or more consistent access to forage.
Relaxation and Lip Drooping
Sometimes teeth show simply because the horse is deeply relaxed. When a horse’s lower lip goes slack, it droops away from the gum, and the lower teeth and pink inner lip become visible. This is common during rest, grooming, or after exercise when the horse is winding down. The Equine Facial Action Coding System describes this as a distinct movement where the lower lip relaxes completely, causing the lips to part and teeth to show passively. There’s no tension anywhere in the face, the ears are neutral or slightly to the side, and the horse’s overall posture is loose. This is the equine equivalent of zoning out on the couch.
Trained “Smiling” Behavior
Some horses learn to curl their upper lip on cue through positive reinforcement training. Using clicker training and food rewards, handlers can shape the natural lip-curling motion into a trick performed on command. If you see a horse “smiling” on social media or at a demonstration, it’s almost always a trained behavior rather than an emotional expression. The horse isn’t happy or amused in the way humans associate with smiling. It’s performing a physical action it has learned produces a reward.
How to Read the Full Picture
The teeth themselves don’t tell you much in isolation. What matters is everything happening around them. A quick checklist of context clues:
- Head position: Raised with nostrils flared suggests the Flehmen response. Extended forward toward a target suggests aggression.
- Ear position: Ears pinned flat back signal aggression or pain. Ears neutral or forward suggest the horse is relaxed or simply processing a smell.
- Facial tension: A tight jaw, strained muscles around the eyes, and a clenched mouth point to pain. A loose, droopy face points to relaxation.
- Body posture: A tense, coiled body facing a target means threat. A slack body with a cocked hind leg means the horse is at ease.
- Duration and repetition: Brief, one-off lip curling is usually the Flehmen response or a passing reaction. Repeated teeth grinding, persistent lip curling, or excessive yawning over hours or days suggests a physical or welfare concern worth investigating.