In a place like Yellowstone the rules that humans normally live by are only one set of rules among many. When we leave the roads and villages other rules come into play, rules where creatures who are not always friendly have a say. The largest animal in North America, the bison, lives here and is often ill-tempered. The Park hosts a wide range of pathogens—viruses, bacteria, and parasites, including one that gives you bubonic plague. Yellowstone has two species of poisonous snakes, almost every species of deer in North America, grazing animals, lions, wolves and bears. Some Yellowstone creatures are profoundly dangerous; they eat people. It’s not surprising that a land with such astounding landscapes also has astounding lifeforms. That is what makes life in Yellowstone real and gives it quality.