It is the stirrup, a bone in your middle ear. Inside, You'll Find: A marine mammal with an outstanding sense of hearing Diagrams, a time line, photos-and the letters from A to Z in sign language Surprising, True facts that will shock and amaze youIt is the stirrup, a bone in your middle ear. Inside, You'll Find: A marine mammal with an outstanding sense of hearing Diagrams, a time line, photos-and the letters from A to Z in sign language Surprising, True facts that will shock and amaze you