Well, the Bible says that Eve was deceived, and that Adam was responsible for the first sin. So I wonder if Eve believed Satan and had less reason to know better. She misrepresents what God said - "can't touch" - and some commentators believe Adam told her what God had said rather than her hearing it first hand, so since Adam's right there and could have corrected the snake or otherwise challenged him, but Adam didn't, maybe Eve was testing Adam's word more than God's.
Some commentators argue that Adam is responsible because he wasn't deceived, but he didn't defend God when the snake spoke, either. Perhaps it could be argued that while Eve was decieved - confused - Adam set himself up as God's judge when he should have been God's defender. Or Eve's defender, for that matter - if Satan did
not deceive Adam, then Adam knew the tree was most likely deadly, yet he let Eve eat first. If Eve had died, Adam might have been the first to say, "Am I my brother's keeper?"
The Bible consistently identifys Adam as the first sinner, so the first sin was not the actual eating of the fruit.
Sheryl