Sierra paused right in her tracks and listened carefully to what the professor was saying. Her brown eyes scanned the area, and she imagined rocks, roots, and other things that may or may not actually be there. Just thinking about the concept made her head hurt, and so she turned back to the professor with her hand raised in the air.

"It's a charm used to hide something, like a magical creature or object from a Muggle," she answered. "It actually causes an object to blend into whatever is behind it." Again, she glanced around the area, wondering just what, if anything, was lurking behind a Disillusionment Charm.