We tend to describe our immune systems with military metaphors. Pathogens invade our bodies, knock down our defenses, and try to kill us dead. We fight back with hand sanitizer and mild germ-related panic. Or we go nuclear and blast them with antibiotics. Ed Yong [1]’s beautiful, smart, and sometimes shocking new book I Contain Multitudes [2]: The Microbes Within Us and a Grander View of Life will make you take a deep breath.