Hi John, I asked my vet this before as my dog Bobby does this sometimes, She said it's normal in dogs, sometimes they eat grass when they have an upset stomach, sometimes they just do..
You meed to remember that dogs do everything from instinct, they do not have a consience nor free will as a human does, therefore they don't go outside and actively decide to eat grass because they like the taste, they eat it because their instinct is telling them their body needs it. Cats eat grass too, usually to help get rid of a hairball,.