Dogs have been known to eat grass for several reasons. Maybe people believe that dogs eat grass when they have an upset stomach. Eating the grass usually makes dogs vomit a little later on. Some dogs have been known to just like to eat grasses. It's not uncommon and it's not something to be worried about.

Dogs can have upset stomachs just like we can. When their stomach gets full of air or food that upsets it stomach it will eat grass so it can throw up the excess.