This article explores the work of psychologist Gordon Gallup, Jr., during the 1960s and 1970s on mirror self‐recognition in animals. It shows how Gallup tried to integrate the mental “self‐concept” into an otherwise strictly behaviorist paradigm. By making an argument from material culture, the article demonstrates how Gallup's adoption of a self‐concept is best understood as a product of his sustained analysis of the workings of the mirror as a piece of experimental apparatus. In certain situations, the stimulus properties of the mirror changed dramatically, a shift that Gallup thought legitimated the positing of a self‐concept. For this reason, Gallup supposed he could use a mirror to provide an operationalized concept of the self, that is, produce a definition that was compatible with behaviorist experimental norms. The article argues that behaviorism was more supple and productive than is often assumed, and contained resources that could align it with the “cognitive revolution” to which it is most often opposed.