E.B. Bartels has had a lot of pets—dogs, birds, fish, tortoises. As varied a bunch as they are, they’ve taught her one universal truth: to own a pet is to love a pet, and to own a pet is also—with rare exception—to lose that pet in time. But while we have codified traditions to mark the passing of our fellow humans, most cultures don’t have the same for pets. Bartels takes us from Massachusetts to Japan, from ancient Egypt to the modern...