Dogs and cats eat grasses to recover from a illness or a injury, even to maintain their health. They can almost survive on a grass diet. However this is not perfect for them. If you have a indoor pet they of course don't have access to grass, so they may start to eat your houseplants. And this can be dangerous for them if they ingest the wrong ones. So why not grow your own tiny indoor garden for them. Wheat grass contains the highest concentration of nutrients for them. Both cats and dogs love it.