My dog Mel, loves to eat grass lawns. I usually tell him to stop because it might upset his tummy.
There is this article that explains why:
The ingestion of grass does make some dogs vomit, but it’s unclear if it was the grass that gave the dog the upset stomach to begin with. They just like the way it tastes. Remember, dogs enjoy all sorts of things that disgust the human palate—dirty socks and gristle from the trash can, anyone?