Seeking a richer Catholic understanding of passion vs intellect as it applies to our first parents I was tempted to answer this question about freewill and Adam and Eve but I chose not to because all I've got it conjecture and I'm not even sure if it's not borderline heresy on the matter.  What I'd like to know is if what I would have answered lines up with Catholic thought.

I would have said:


  Adam and Eve could sin because they chose to follow their intellect and made a rational decision that being like God was in fact a good idea. They could give in to temptation, without following their passions (as they had complete self-mastery in this regard) for the same reason that Lucifer could want to be like God. 


Then I might have gone on with:


  In this way God shows us the difference between following divine law (i.e. not eating an apple because God commanded it) and not following natural law (i.e. not intentionally eating (or giving someone) a poisoned apple because it will cause death) and divine law is a kind of law that can be violated without giving into your passions.  That is to say, an act of pure intellect can violate divine law, but violating natural law requires giving in to the passions (intentionally diverting your will from your intellect).


If someone could run that through their Catholic fluff and heresy parser and give me a readout I'd sure appreciate it before I go and tell it to my Religious Ed. kids, should the matter arise.
The short answer to your question is to review the Haydock Commentary of the 3rd Chapter of Genesis.

I feel like I should add more, but I'm not smart enough to top the incomparable Haydock commentary. Here are a couple short, relevant snippets:


  Ver. 1. Why hath God? Hebrew, "Indeed hath God, &amp;c." as if the serpent
  had overheard Eve arguing with herself, about God's prohibition, with
  a sort of displeasure and presumption. St. Augustine thinks, she had
  given some entrance to these passions, and the love of her own power,
  and hence gave credit to the words of the serpent, de Gen. ad lit. xi.
  30. She might not know or reflect that the serpent could not reason thus, naturally; and she had as yet, no idea or dread of the devil.
  (Lombard, 2 Dist. 21.) This old serpent entered into the most subtle
  of creatures, and either by very expressive signs, or by the motion of
  the serpent's tongue, held this delusive dialogue with Eve. Moses
  relates what happened exteriorily; but from many expressions, and from
  the curse, ver. 15, he sufficiently indicates, that an evil spirit was
  the latent actor. (Haydock) --- Of every tree. Satan perverts the word
  of God, giving it an ambiguous turn: in doing which, he has set
  heretics a pattern, which they follow. (Menochius)
  
  Ver. 5. God. The old serpent's aim is, to make us think God envies our
  happiness. (Haydock) --- Or he would have Eve to suppose, she had not
  rightly understood her maker, who would surely never deprive her of a
  fruit which would give her such an increase of knowledge, as to make
  her conclude she was before comparatively blind. (Menochius) --- As
  gods, Hebrew Elohim, which means also princes, angels, or judges. It
  appears, that our first parents had flattered themselves with the
  hopes of attaining a divine knowledge of all things. (Calmet)