Answer:
What is that which, while it lives, constantly changes its habit, that is buried before it is dead, and whose tomb is valued wherever it is found?
What lives where it cannot breathe and has a hole in its back
A spent round or a slimy critter.
What has a horn but does not work?
When they are caught, they are thrown away. When they escape, you itch all day.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.