Gastric bypass surgery is a specific medical technology that alters the body in ways that force patients to fundamentally change their eating habits. When patients enrol for surgery, they enter a learning process, encountering new and at times contested ways of sensing their bodies, tasting, and experiencing hunger and fullness. In this paper, we explore how patients begin to eat again after gastric bypass surgery. The empirical data used here are drawn from a Danish fieldwork study of individuals undergoing obesity surgery. The material presented shows how the patients used instructions on how to eat. We explore the ways in which diverse new experiences and practices of hunger and fullness are part of the process of undergoing surgery for severe obesity. New sensory experiences lead to uncertainty; as a result, patients practice what we term mimetic eating, which reflects a ‘sensory displacement’ and hence a rupture in the person's sense of self and social relations. We suggest that eating should be conceptualised as a practice that extends beyond the boundaries of our bodies and into diverse realms of relations and practices, and that changing the way we eat also changes the fundamentally embodied experience of who we are.