The ingestion of grass can induce vomiting in the animal acting, as many comment, "of purgative".
It is curious to see our dog selecting a specific type of grass on his usual walk, a vegetable intake that, no matter how hard we think, does not have a common cause in all animals.
The dog is preferably carnivorous but in its natural state, when ingesting the game it hunted, it took a part of plant matter, which was found in the digestive system of hunted herbivores.
This is one of the theories as to why dogs continue to eat grass due to an “innate eating habit”.
Other theories defend that the animal ingests a certain amount of plant matter to induce vomiting, popularly referred to as the "purgative effect." Supposedly the animal, being "strange" in its digestive system, ingests grass and vomits, thus ending its ills.
The truth is that we can find animals that ingest a large amount of grass and does not cause the slightest effect on them, and those in which the relationship causes an effect is evident: they eat grass and in a more or less short period of time, they vomit.
In one way or another, the ingestion of grass should not worry the owner, except in cases where vomiting occurs too frequently, in which case we should go to the vet.
What we can affirm is that those animals whose diet is appropriate to their age, condition and activity, those that consume quality food, see this behavior diminished.
Video: Why Do Dogs Eat Grass?