“Grass contains considerably less protein than meat. A herbivore must, therefore, consume more food to obtain the same nutrients as a carnivore. Nutrients in meat are rather easily available and digestible, but this is not the case for plants. Their nutrients must be released by first patiently grinding through their cell walls, for plant cells are protected by a very tough covering of cellulose; also, natural toxins or other unpalatable substances can make a plant inedible. Great adaptive changes were needed in the digestive organs and teeth before grazing animals could become nearly as successful as the carnivores. Although the numerous sharp teeth of the insectivores indeed permitted these animals to seize and tear up their small, active prey, they failed miserably for chewing grass. To do this efficiently, broad chewing surfaces covered with hard cusps for grinding up plants were much more important than sharply pointed teeth.”