[Wendy] also wore her mother’s long bathrobe and had this crazy-looking fur thing wrapped around her neck. It had eyes, paws, a tail and everything.
“Animals are for loving, not wearing,” I told her.
“I know it,” said Wendy, “but this thing is very old. It belonged to my grandmother. And in those days they didn’t know about ecology.”
– Judy Blume, Blubber
Books: they are made from animals.
These days, most books are actually made of some combination of paper, cloth, and/or plastic. Animal products are rare, and mostly consist of various kinds of leather used in fancy-schmancy gift editions (or attempted forgeries). Back in the day, however, animal products were more common than not, and knowing your animals is a big part of knowing how to navigate the world of rare books.