Question Five of Chapter Six of the Third Decade
Why the demon, having attacked the woman Eve, tempted her in the form of a serpent and by vocal speech
It is asked why the demon did not tempt Lady Eve by an interior suggestion but by vocal speech, and why he did so in the form of a serpent rather than that of the other reptiles or animals.
To this it is answered that, although with God permitting it the devil could have tempted the human being through interior suggestion and phantastic persuasion, he was nevertheless permitted to tempt only through the persuasion and exterior appearance of vocal speech. Thus he disclosed through the tongue the hidden condition of his malice and presented himself manifestly and fittingly to the first parents.
He wished to appear and speak in the form of a serpent rather than that of the other reptiles or animals because, among every genus of venomous serpents, as Albert says in Book XXI On Animals, the serpent is craftier and more cunning. Scripture also says: “But the serpent was craftier”—that is, more prudent—“than the other living creatures of the earth.”
The devil also added to the prudence and malice of the serpent, because, as Augustine says in Book XI On Genesis, the devil filled that serpent and mingled his own spirit with it.
These things are from Henry of Assia upon Genesis.