The Serpent, to my interpretation, was pain.

As we reread Genesis 2...we immediately understand WHAT is 'crafty' about the serpent's question in Genesis 3. God did NOT in fact say in Genesis 2, 'You MUST NOT EAT from any tree in the garden' (3:1). What God did say was almost exactly the opposite: 'You ARE FREE TO EAT from any tree in the garden' (except the tree of the knowledge of good and evil, 2:16). The vocabulary of God in Genesis 2 indicates freedom and blessing. The vocabulary of the serpent in Genesis 3 indicates prohibition and restriction. The serpent's ploy is to suggest to the woman that God is really not so good after all. He shifts attention away from all that God in his generosity has provided for his creatures in creation and onto the one thing that God has for the moment explicitly withheld.

I hate and fear snakes, because if you look into the eyes of any snake you will see that it knows all and more of the mystery of man's fall, and that it feels all the contempt that the Devil felt when Adam was evicted from Eden. Besides which its bite is generally fatal, and it twists up trouser legs.

("The Return Of Imray")

Some flow'rets of Eden ye still inherit, / But the trail of the serpent is over them all!

The temptation was an absolute truth and the serpent was the tempter. For his insolence the snake was punished and condemned to crawl on its belly forever.

To the pain.