A Bookend is a large book with sharp teeth that comes out of book shelves and flys toward Mario. The green books dissapear if they hit anything, including Mario. They are found in Big Boo's Haunt in the game Super Mario 64.
He often only comes out if Mario gets too close to him, and he gets faster as he gets closer to Mario. If Mario can jump on the book, it will release a blue coin. If Mario is unsuccessful, he lose two life points.