Ambrose of Milan

But since all creatures are subject to passions, lust, with the stealth of a serpent, has crept over man's affections: well therefore has holy Moses represented lust under the similitude of a serpent; for it creeps upon its belly like a serpent, not walking on foot, nor raised up on legs, gliding along by the sinuous contortions, as it were, of its whole body. Its food, as that of the serpent, is earthly, for it knows not heavenly food, but feeds on carnal things, and changes itself into various kinds of desire, and bends to and fro in tortuous wreaths. It has poison in its fangs, whereby the belly of every luxurious man is ripped up, the glutton is slain, the licker up of dishes perishes.