Harvey Riley, The Mule: A Treatise on the Breeding…
“ A mule, however, will eat almost any thing rather than starve. Straw, pine boards, the bark of trees, grain sacks, pieces of old leather, do not come amiss with him when he is hungry. There were many instances, during the late war, where a team of mules were found, of a morning, standing over the remains of what had, the evening before, been a Government wagon. When two or more have been kept tied to a wagon, they have been known to eat each other's tail off to the bone, And yet the animal, thus deprived of his caudal appendage, did not evince much pain. ”
