Like I said, I'm no artist. Really, I'm the opposite of artistic. But I've always loved this illustration, the way that Mayer did the close-up of the little girl, so we know how small the fly is, how her eyes are calm and serene, but the possum's eyes are frightened (because SPOILER ALERT that blue bottle fly is really the Sly Swamp Devil, who we all know will jump down inside a person and steal her soul away). And even as a kid, I thought the color of Liza Lou's skin was beautiful.
While talking to my daughter, I pointed out the things I liked---her skin, her eyes, the possum's eyes, and then I pointed to the hands. I think the hands are just beautifully drawn, and told her that. She pointed to the heel of Liza Lou's hand, the one holding the cork, and said, "I think that looks like two kidneys!"
Well. So it does.