What is a one-sentence summary of the following article?
Horses are often happy when they graze. If you notice your horse walking around the pasture and slowly grazing, this is a good indication that they are happy. Unhappy horses may stand still or gallop along fence lines. If you see your horse rearing their front legs upward or pawing/scratching at the ground, they may be happy. Ultimately, these are signs that the horse is in a playful mood. Unhappy horses won't play. Observe how your horses interact together. If two or more horses are engaged in grooming behavior, they're likely relaxed and happy. Ultimately, grooming is a behavior horses will do when they are at ease and want to bond with others. When a horse breathes out rapidly through its nostrils and makes a light snort sound, they're likely happy. This is often a sign that a horse is relaxed and satisfied. The horse may make this sound while they're being ridden or interacting with a person or another horse. If your horse does a light nicker while being alert, having a raised head, and pointing their ears in your direction, they may be happy. Your horse may nicker when you're bringing food or treats to them. They may also nicker if they're excited to see you or another horse. If nickering becomes more intent, high pitch, or seems stressed, it could be a sign your horse is unhappy. Cribbing is when a horse bites something with its teeth, arches its neck, and then makes a sort of grunt. Cribbing is a sign that a horse is stressed out and unhappy. If your horse chews, gnaws, or cribs, it is likely stressed. You should consult a veterinarian if your horse exhibits this behavior often. Horses will usually bite onto stall doors, poles, or other hard objects when cribbing. Horses are herd animals and like to be near other horses usually within 5 to 10 feet (1.5 to 3.0m). Horses that are unhappy will be off by themselves, intentionally isolating themselves from the herd.

Summary:
Observe whether the horse is grazing. Watch to see if they are rearing or pawing. Note if horses are grooming each other. Listen for snorting sounds. Pay attention to nickering. Watch to see if the horse is crib-biting. Watch your horse's herd behavior.