In almost all cases, it can be said that dogs in fact don’t eat grass, but drink the moisture that it contains (up to 80% moisture). The moisture in grass is very tasty and well-filtered, and unlike tap water, it does not contain chlorine, calcium, etc.
You may already have experienced that your dog doesn’t drink from the fresh bowl of tap water put before himbut, immediately afterwards, will drink from the rainwater outside.
As already mentioned , drinking is difficult for a dog and extracting moisture from solid substances very normal. As a carnivore it cannot extract nutritional substances from grass, but can extract moisture from it.
Contrary to cats, a dog doesn’t need to eat grass to vomit. That is a remainder from its ancestor, the wolf, who vomits food for pups when they start to eat solid food.