Books 9 and 10 of Milton's Paradise Lost deeply explore the theme of appearance versus reality. Let's look at a few of the ways this theme appears to help you get started on this question.

In book 9, Satan, who appears as a serpent, deceives Eve. You should note how he presents "reality" to her, twisting it so that Eve sees only appearances. Satan tricks her into false thoughts about God and herself and the fruit of the tree. That fruit looks very good to Eve, for she now thinks that she will have knowledge if she eats it and that such a thing cannot be a sin worthy of punishment. Satan even convinces Eve that God wants her to eat the fruit to prove herself. This could not be further from the truth, of course, but Satan weaves a whole net of appearances that are directly opposite of reality.

The theme continues in book 10. Adam and Eve make their excuses, which are merely that. An excuse is only an appearance, not reality. Back in hell, Satan and his fallen angels turn into a dragon and serpents as punishments for what Satan has done. The appearance has become the reality.