" A Glass Cat!" exclaimed Ojo, astonished. "Yes; she makes a very pleasant companion, but admires herself a little more than is considered modest, and she positively refuses to catch mice," explained Margolotte. "My husband made the cat some pink brains, but they proved to be too high-bred and particular for a cat, so she thinks it is undignified in her to catch mice. Also she has a pretty blood-red heart, but it is made of stone—a ruby, I think—and so is rather hard and unfeeling. "

― L. Frank Baum , Oz: The Complete Collection (Oz, #1-14)