Jamieson, Fausset & Brown

the woman said, We may eat of the fruit of the trees of the garden--In her answer, Eve extolled the large extent of liberty they enjoyed in ranging at will amongst all the trees--one only excepted, with respect to which, she declared there was no doubt, either of the prohibition or the penalty. But there is reason to think that she had already received an injurious impression; for in using the words "lest ye die," instead of "ye shall surely die" [Gen 2:17], she spoke as if the tree had been forbidden because of some poisonous quality of its fruit. The tempter, perceiving this, became bolder in his assertions.