There is a tendency, particularly in health discussions, to reduce everything to a simple question of what is good and what is bad. Parasites belong firmly in the latter category, at least according to the conventional story. But the deeper I get into the terrain model, microbial ecology, fasting, and the strange adaptability of living systems, the less satisfying that binary becomes. What if the organism we are calling the problem is sometimes part of a much larger process? And what happens when we start asking not simply what an organism is, but what it is doing, and why?