I don't think this is true- every dog I've had eats grass frequently and it doesn't usually cause them to throw up. Also- dogs can throw up on demand at any time, they don't need anything like grass to help them. This is because it is the natural way that female dogs bring home food for puppies, they vomit up the food to share it with them.
I'm pretty sure dogs sometimes vomit on purpose with the explicit goal of sharing food with humans, and/or just to eat it again for fun out of boredom. When my dog is bored he will often start preparing to vomit, and if I tell him 'no', he will stop.
I think humans have a hard time understanding animal behavior, and consistently underestimate their intelligence because we don’t understand or relate to their motivations and interests.
We take our values and motivations as objective facts, and don’t even consider that maybe dogs enjoy eating grass, and also aren’t that interested in the weird sounds humans like to make with their mouths.
Not sure about the latter statement. Our dog is very interested in any keyword verbalised by us that may relate to receiving food or a walk or a ride in the car (from pretty much any corner of the house). She appears to be permanently listening to every sound we make.
She probably does. Wolves in the wild eat the undigested stomach contents of their herbivorous prey. This food source is missing from modern dog food, so domestic dogs make up for it by eating plants directly.
