Aristotle claims that in making an animal, nature acts like a “good housekeeper” who “is accustomed to throw out nothing from which it is possible to make something useful” (744b16–17). How does nature act when it “make[s] something useful” in these cases – and does it differ from other ways it acts? I defend two main claims. The first is that Meteor. 4.2’s distinction between two sorts of ‘concoction’ processes offers an underappreciated source of evidence for answering this question. My (...) second claim concerns the nature of those processes and the ends they realize. While they are both the ends of their respective types of concoction, they differ in that some essential (process-defining) features of the second end – but not the first – are supplied by what the capacities of the “underlying” patient (on which the agent acts) are for. The result is a distinction between two kinds of end-directed efficient causation. (shrink)