As Carly reads the words of the spell, she will feel some of the book's dark power move through her - whatever she is doing, it seems to be affecting her, personally. It's a feeling that starts in her head and chest and rolls down to her toes-

-and, as she completes it, her shadow will break free of her, it's vague reflection of her silhouette starting to move around of its own accord, without much direction or purpose. As such, it won't be long before it starts wandering out of sight.