We were looking at titles of the books in our neighborhood's little library, all standing erect on a shelf. Dorothy referred to a book that she thought was for someone older than her, but I said, "This is the real meaning of You can't judge a book by its cover." Dorothy responded, "Well, in this case, it's You can't judge a book by its spine."
I looked at an image of a flower and suggested that it was a lily of the valley. Dorothy immediately chimed-in, "Oh, I know what a lily of the valley is: a highly poisonous woodland flowering plant." (Thanks again to her podcasts.)