No one really knows why dogs eat grass, in part because there’s been very little scientific study of this behavior in dogs. In the absence of such analysis, many theories have been floated. Some scientists believe, for example, that eating grass is a dog’s attempt to compensate for something lacking in his diet—for example, a lack of sufficient fiber, vitamins or minerals.
Others argue that eating grass is a remnant of undomesticated dogs’ behavior, since many varieties of wild dogs have been observed eating grass. Dogs in the wild are omnivorous, eating both meat and plant materials, for example, and domesticated dogs are simply replicating the behavior of their ancestors, according to the proponents of this theory. Still others speculate that dogs just like the taste of grass, and some believe eating grass is a dog’s attempt to induce vomiting, perhaps to remove something that’s upsetting his stomach.