Because we know the difference between good and evil - bible excerpt - the serpent talking to Eve in the Garden of Eden:
Did God actually say, ‘You[a] shall not eat of any tree in the garden’?” 2 And the woman said to the serpent, “We may eat of the fruit of the trees in the garden, 3 but God said, ‘You shall not eat of the fruit of the tree that is in the midst of the garden, neither shall you touch it, lest you die.’” 4 But the serpent said to the woman, “You will not surely die. 5 For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil.” 6 So when the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was to be desired to make one wise,[b] she took of its fruit and ate, and she also gave some to her husband who was with her, and he ate. 7 Then the eyes of both were opened, and they knew that they were naked. And they sewed fig leaves together and made themselves loincloths.