John Chrysostom

You see, since Cain perpetrated practically the same evil as the serpent, which like an instrument served the devil's purposes, and as the serpent introduced mortality by means of deceit, in like manner Cain deceived his brother, led him out into open country, raised his hand in armed assault against him and committed murder. Hence, as God said to the serpent, "Cursed are you beyond all the wild animals of the earth," so to Cain too when he committed the same evil as the serpent.