A cow is not "matter" in the conventional sense but, rather, a collection of m00ons. Bet ya didn't know that :p
The whole eating grass thing is a front, cows know that if humans found out they really use a simple form of nuclear fusion they would all be experimented on (rather than say, killed and eaten)
The byproducts of the reaction going on inside the cow are "milk" and "shit"
Cows eat grass but secretly throw it up at night. Grass does not taste good.
Thou shalt love thy cow lest it explode in a ball of fire.
its really just a collection of m00ons