Catechism of the Catholic Church writes:
Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God's law. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart133 do not diminish, but rather increase, the voluntary character of a sin.
Contrary to the claims of the now-departed author of the thread, Eve's lying, and ANY miscommunication in the GOE, was NOT sin.
Sin requires knowledge that there IS a sin. Before eating of the tree, there was no knowledge of Good or Evil.
Oh, and of course, I am not too much of a literalist, but if anyone wants to discuss this 'first sin' there is at least one good reason not to get too sure of oneself.