In the popular mediaeval tradition, as contrasted with official theology, there are many legends which associate saintliness and martyrdom with kindness to animals: even Jerome has his lion, to say nothing of Androcles. Vicious animals in that tradition were like the Gadarene swine, inhabited by demons. They might be brought to trial for their misdeeds and punished by the extremest of penalties—a form of distinction which, no doubt, they would willingly have foregone. Domesticated animals, in contrast, were the dwelling places of angels. The merely wild, but not the vicious, were spiritually uninhabited. Saintliness was demonstrated by a capacity to drive the demons out of the vicious—as some of the biographers of Francis of Assissi report that he tamed the wolf of Gobbio—and ordinary human virtue in domesticating wild animals, thus making of them a fit residence for angels.
(John Passmore, "The Treatment of Animals," Journal of the History of Ideas 36 [April-June 1975]: 195-218, at 199)