I think I must be missing something. From what I can get out of this Aristotle "Metaphysics of Explanation" shite so far, humans are the official cause of pianos, the purpose of a duck is to reach duckhood and srtive to be the most ducky duck it can be, and when you pour milk into a cat it becomes more cat, but when you pour cat into milk, it does not become more milk. HUH???? Well, maybe this exam will be more fun than I've anticipated...