First, to read Scripture literally is to read it as literature. This means that we are to interpret the Word of God just as we interpret other forms of communication—in the most obvious and natural sense. Thus when Moses uses the symbolism of a snake, we do violence to his intentions if we interpret him in a woodenly literal fashion.
Furthermore, a literalistic interpretation does as much violence to the biblical text as a spiritualized interpretation that empties the text of all objective meaning. If the historical Adam and Eve did not eat the forbidden fruit and descend into a life of habitual sin, resulting in death, there would be no need for redemption. If, on the other hand, Genesis were reduced to an allegory conveying merely abstract ideas about temptation, sin, and redemption, devoid of any correlation with actual events in history, the very foundation of Christianity would be destroyed.
Finally, when the prophet Moses describes Satan as an ancient serpent and the apostle John describes him as an ancient dragon, they do not intend to tell us what Satan looks like. They want to teach us what Satan is like. (Dragons, after all, are the stuff of mythology, not theology.) If we think of Satan as either a slithering snake or a fire-breathing dragon, we would not only misunderstand the nature of fallen angels, but we might also suppose that Jesus triumphed over the work of the devil by stepping on the head of a snake (Genesis 3:15) rather than through his passion on the cross (Colossians 2:15).
In short, Eve was not deceived by a talking snake. Rather Moses used the symbol of a snake to communicate the wiles of the evil one who deceived Eve through mind-to-mind communication—precisely as he seeks to deceive you and me today.
For further study, see Hank Hanegraaff, The Apocalypse Code: Find Out What the Bible Really Says About the End Times and Why It Matters Today (Nashville: Thomas Nelson, 2008).