Knowing when a dog is happy is easy, but spotting fear is a lot harder, as Michele Wan, a certified applied animal behaviorist, and her colleagues showed in research examining whether people's perceptions of dogs' emotions vary according to experience. In the study, published in PLOS ONE in 2012, volunteers—who were grouped as having little or no experience with dogs, having lived with a dog at some point, or working with dogs for more or less than 10 years—watched short video clips of dogs. They then categorized the dogs' emotional state and noted which body parts tipped them off. Because the videos had no sound, participants had to rely on behavior to label a dog as, say, fearful or happy. These videos were not just any videos. They had been prescreened by dog-behavior experts whose schooling or professional experience had trained them to make science-based assessments of animal behavior.

Happy dogs proved easiest to identify. Even people with little dog experience could watch a dog frolicking in the snow or rolling joyfully on its back and describe that dog as happy.

But fear was different. Study participants who were dog professionals did a better job identifying fear compared with both dog owners and people with little dog experience. “It did not matter whether the dog professionals were relative newcomers to the field, had worked with dogs for less than 10 years, or were longtime professionals with 10 or more years of experience,” Wan adds. “They had the same proficiency in identifying fear.”

One reason that the dog professionals did so much better could be that they looked at more dog body parts for clues, such as the eyes, ears, mouth and tongue, whereas nonprofessionals looked at fewer body parts and were less likely to tune into dogs' facial features.

Fortunately, you can learn how to notice and interpret subtle canine behaviors. Indeed, even if you live with the most happy-go-lucky dog on the planet, fear should still be on your radar, especially if your dog ever interacts with other dogs. Recognizing fear in another dog can help you know to give that dog space; the owner can take it from there.

What does fear look like? It can include a wide variety of body parts and postures. Wan and her colleagues explain that “fearful dogs are said to reduce their body size—crouching into a low posture, flattening their ears and holding their tails in a low position. Shaking, yawning, salivation, freezing, panting, paw lifting and vocalizing are examples of other behaviors that have been associated with fear in dogs.”

It is possible to help dogs become less fearful. Noticing fear and related behaviors is the first step; identifying and modifying an animal's perception of fear-inducing stimuli is just as important. Picture a dog that is afraid of new people coming to the home, everyone from the postal delivery worker to your best friend. But now, when anyone comes to the home, the dog gets pieces of its most favorite food. Through counterconditioning, visitors gradually assume a new meaning as the dog associates people coming over with a good thing, in this case yummy food. As the dog's emotions shift, so, too, does its behavior—fearful postures fade away to reveal a dog anticipating something good, a dog essentially saying, “OMG!! A NEW PERSON IS HERE!! YES!!” A happy dog is born.