What sorts of moral challenges do interspecies encounters engender in laboratory science? Animal Ethos draws on extensive ethnographic engagement within and beyond academic labs, where the lives and deaths of a host of species deemed essential to experimental research enable broader imaginaries of scientific progress. Whereas much has been written on core bioethical values that inform proper and regulated lab behavior and decorum, Lesley A. Sharp lays bare the importance of attending to quotidian and unscripted responses to animals among lab personnel. Animal Ethos exposes the rich—yet poorly understood—moral dimensions of daily lab life, where serendipitous, creative, and unorthodox responses evidence concerted efforts by researchers, animal technicians, veterinarians, and animal activists to transform animal laboratories into moral scientific worlds.