Can we survive on grass? Like the cows? :)?

Not directly, no. Humans cannot get any nutritional value from grass. We can, however, survive on yeast or other simple single-cell organisms, as long as we get additional minerals and vitamins.

The human digestion system can not digest grass. Boiling can help in making some kind of soup or tea, but it's not very palatable. If you consider mustard greens, spinach, dale, or lettuce a grass, of course you can become a vegetarian and have strong bones like a cow. But don't forget, you need protein like beans too, which cows also can eat. You would tire of that diet quickly.

no, we don't have the enzymes to digest grass. So grass won't give us nutritional benefits. I think it's Beta-galactosidase that's required to hydrolyse cellulose (grass) to monosaccharides.