The hare-shaped hole
(Book)

"Hertle and Bertle were always a pair, though one was a turtle and one was a hare. They were utterly buddies, and best friends forever, and whenever you looked, you would find them together... until quite unexpectedly... the end came. When Hertle disappears for good, Bertle can only see a Hertle-shaped hole where his friend should be. He pleads with it, get angry with it, but the hole still won't bring his Hertle back. It seems like hope is lost... until Gerda the kindly bear finds him. She explains that he must fill the hole with his memories of Hertle. And slowly... Bertle begins to feel a little bit better."--,Amazon.com.