Whenever my dog starts munching on grass in the backyard, I get worried. “Are you feeling okay?” I ask him, receiving an excited stare and wagging tail in response because he thinks every time I speak means a future treat or walk. Sometimes he eats grass by the mouthful and promptly vomits; other times he nibbles and his stomach contents remain intact. I’ve always heard that a dog eating grass signals an upset stomach, but I’ve seen my dog and others like him eat it so indiscriminately, there must be more to it than indigestion. So what drives dogs to go lawn dining?

Are They Craving Greens?
The truth is, no one’s entirely sure why dogs eat grass. Theories abound, but most experts subscribe to one of two schools of thought. The first is that dogs are actually predisposed to craving grass. Back before they were domesticated, wild dogs regularly fed on plant-eating animals, which meant their diets indirectly included lots of greens.

Commercial dog food is supposed to include adequate plant and animal nutrients, but as all of us know, there’s a big difference in satisfaction levels between swallowing a multivitamin and eating vitamin-filled foods. Both fulfill nutritional needs, but only one fulfills a craving for veggies. Even if dogs are getting greens in dog food form, their instincts might pull them toward grass every now and then to get the same flavors their ancestors enjoyed courtesy of their prey.

Is It Always a Stomachache?
The other popular idea is the aforementioned theory—that dogs ingest grass when they feel sick. The texture of grass is slightly irritating, so if they already feel nauseated or pained, grass gives the extra push they need to get rid of whatever they’ve eaten that’s sickening them.

Dogs probably don’t do this because of a complex chain of thoughts—i.e., “My stomach hurts, so I better eat some grass for medicine.” More likely it’s that, like people, they can remember what works and what doesn’t when they’re ill. Just like we learn through behavioral conditioning that curling up with a cup of peppermint tea can ease a troubled tummy, dogs learn that eating too much grass causes them to upchuck. So when there’s something inside of them causing problems, the instinct to release it from their system kicks in and they go for the tried-and-true method.

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