It being called "that old serpent" shows that it had the characteristics of that serpent in Eden, in the sense of being a deceiver, as the serpent was. Similarly, "the sting of death is sin" (1 Cor. 15:56), but that does not mean that death is a literal snake.
Hali moja, "Uchungu wa mauti ni dhambi" (1 Kor. 15: 56), Lakini hiyo haina maana ya kuwa mauti ni nyoka yule. Anatabia ya nyoka, kwa kuunganika na dhambi.