This article presents an analysis of data from over 200 accounts of, and responses to questions about, how animals feature in people's lives. The accounts were generated by a Mass Observation Project (MOP) directive on "Animals and Humans." The MOP, based at a UK university, sends out two or three directives a year, asking correspondents to write in response to a series of questions and prompts. The "Animals and humans" directive began with the question, "What do animals mean to you?" followed by a range of prompts about respondents' experiences of animals. The paper is specifically concerned with issues of how language both reflects and contributes to typologies of living creatures. It presents a qualitative analysis of some of the themes that emerged from responses to the directive, as well as a more quantitative analysis of the words chosen by respondents to denote different kinds of animals. Using these different methodological approaches, it focuses on how moral ambiguity is expressed and the ways in which categories and meanings shift depending on linguistic context. These methods complement each other, with the computer-assisted linguistic analysis providing a different and more quantitative method of revealing aspects of people's values, attitudes, and assumptions as they report on the role of animals in their lives. Overall, the paper shows how a corpus linguistic analysis can demonstrate the permeability of categories and boundaries, and the moral ambiguity toward animals that is revealed in the way language is used.