Personally, we like snakes—but we can't escape that fact that in literature, snakes are almost never a good thing.
And they sure aren't good in Fallen.
I this book, our reptilian friends are associated with Cam. For example, when Cam and Luce are picnicking in the cemetery, a green snake slithers by the pair of them, shedding its skin as it goes. Luce, who doesn't like snakes, finds this disgusting. Then, later, Cam buys Luce a gold necklace with a snake's head on it, which is both unique and potentially a little insulting, since he's making fun of her fear of snakes.
Sure, if you ask Cam, the snakeskin represents the possibility of change. But who asked Cam? We think it's more important that he's so often associated with them—and in rather dangerous ways.
In each of the scenes in which snakes appear, Cam is tempting Luce and trying to charm her into liking him. He's invited her to a fruit-laden picnic when they see the snake for the first time, and then he enchants Luce with a snake necklace he bought for her. We get the uncanny sense that his behavior is supposed to parallel that of the snake in the Garden of Eden, the tempter who lured Adam and Eve away from something good and pure and toward something they weren't supposed to do.
In case you hadn't guessed it, Cam's the snake in this scenario, temping Luce away from Daniel—the goodness she deserves—and trying to convince her to take a bite of that forbidden fruit and get exiled from the garden. Fortunately for Luce, Cam's charms only go so far, and she ultimately rebuffs his attempts, staying tried and true for Daniel.