Genesis 3:1 "Now the serpent was more subtle than any beast of the field which the LORD God had made. And he said to the woman, Yes, has God said, You shall not eat of every tree of the garden?"
Our enemy is subtle. Searching through different Biblical versions and Strong's Exhaustive Concordance for the word 'subtle/subtile' we see that this means crafty, sneaky, cunning, shrewd.
In Genesis 3:1 the devil also twisted the words which God had spoken to Adam. He said "every tree", which may have confused Eve and tricked her into answering him instead of ignoring him.
But when evil is whispered repeatedly into the ear, the heart makes a decision without thinking of the consequences.
God said death was the punishment for eating of the tree of knowledge of good and evil (Genesis 2:17). The serpent said, "You won't die, you will be like gods." The enemy told an out and out lie.
Death is the result of sin. Sin is willful disobedience to what God has spoken. Eve willfully ate the fruit and then handed it off to Adam, who also ate of it. In that instant they both knew they had disobeyed God. But the serpent's tactical interference did not end there.
For when God asked why did they do it, neither took responsibility for their actions. Adam blamed Eve. Eve blamed the snake. The snake was punished as well. Reading Genesis 3:14, 15 we see that snakes had legs! "upon thy belly you shall go". The snake itself became cursed above all animals which God had created. Verse 15 says God put enmity (hatred, hostility) between the woman and the serpent. Not fear, but hatred.
We are not to fear the enemy of our souls but be for ever on the attack and alert for him. Knowing how he works is a good start.