This paper will show how Jacques Lacan's Seminar XI: The Four Fundamental Concepts of Psychoanalysis (1978) uses concepts drawn from the French philosopher of science Roger Caillois' Mask of the Medusa (1964) to explain aspects of analytic theory and therapy. It will first show how Lacan's psychoanalysis can be thought of in terms of Caillois' notion of a transverse science. It will then show how Caillois' theory of insect mimicry can be used to conceptualize the behavior of the analysand as manifested in transference. Finally, it will show how another of Caillois' categories of insect behavior, sorcery, can be used to describe the analyst's actions when providing the client with interpretations. By this, it hopes to point to a broader range of sources for Lacan's thought than are traditionally acknowledged.