I’ve heard something similar to this from professor Peter Kreeft. He also clarifies the meaning of the word we translate as “serpent” to be more appropriately translated as “dragon,” and that it was meant to convey the terrifying nature of the creature that they were confronted with. He doesn’t, however, goes as far as to say explicitly that they were scared for their lives.
But there are certainly other clues to this found throughout scripture. For example, the first reaction everyone in Scripture has at the appearance of an angel is fear, or terror. The first thing angels have to tell people when they appear to them, virtually without fail, is “do not be afraid.” From this, we should be able to figure out is that angels are terrifying. Evil angels that much more for their ugliness.
There are also other clues in the text that demonstrate Adam’s lack of trust. Consider the following. In Genesis 2:16-17, God gives Adam the command not to eat of the tree. In Genesis 2:21-22, God creates Eve. Therefore, God did not give the command to Eve, but to Adam only. This doesn’t mean the command didn’t apply to Eve, just that the command was given directly to Adam, and only indirectly to Eve. The assumption here is that Adam is the one who passed the command on to Eve.
And the command is this: “But of the tree of knowledge of good and evil, thou shalt not eat. For in what day soever thou shalt eat of it, thou shalt die the death.”
But what does Eve say when the Serpent asks her about it? In Genesis 3:3, Eve says: “But of the fruit of the tree which is in the midst of paradise, God hath commanded us that we should not eat; and that we should not touch it, lest perhaps we die.”
God did not command them not to touch it. We could perhaps surmise that Adam, fearing to be alone should Eve take it and die, told Eve not to even touch it, much less eat it.
But notice also that Eve doesn’t say “lest we die,” but rather “lest perhaps we die,” meaning that the question wasn’t settled. They might have died, they might not have. But God told Adam very clearly that he would die if he ate it.
So, one of three things is going on, even before the Serpent enters the scene. Either there is a certain level of distrust between Adam and Eve, such that Eve doubts the certainty of what Adam is telling her. Or, there is a certain level of distrust of God on Adam’s part, such that he is not certain that God’s declaration of death is true. Or, Eve, being terrified of the Serpent, may have felt insecure in her position, weakening it when proclaiming it, for fear of being taken the fool (evidence that this could be the case might be found in the Serpent’s question: “Why hath God commanded you, that you should not eat of every tree of paradise?” This could be read as subtly mocking, as though God were taking advantage of them, perhaps suggesting that “he isn’t forbidden, so why are they?”).
Either way, Eve didn’t receive God’s command directly, hearing it from Adam, and then repeats it back to the Serpent incorrectly. So Eve is starting at a point of disadvantage, a point of ignorance. Not invincible ignorance, but certainly she has a deficiency of knowledge compared to Adam, and so it is to her that the terrifying dragon approaches. She’s in a position of weakness, not by any fault of hers, but as a victim of circumstance. And being less certain than Adam, not receiving the command directly, she is more susceptible to deception. And that fits with the text, she spoke truly when she said the serpent deceived her.
But Adam’s failure first was defending his wife against the serpent, and his second failure was giving in to Eve’s offer. And of course, seeing that his wife ate of the tree without dying, he lost trust in God’s word that he would die. He might also have been afraid of losing his wife, having been alone before.
At any rate, the text is just packed with meaning.