How and why has invertebrate sentience come to be debated by lawmakers, and what does this development tell us about the relationship between scientific knowledge, animal ethics, and the law? This preliminary analysis of this puzzle examines milestones in the production of knowledges about cephalopods (squids, cuttlefish, nautilus, and octopuses) starting in the 1830s and traces the role this knowledge played in the ideas and debates that led to the inclusion of cephalopods in U.K. animal welfare law. New ideas about mind and consciousness emerged from the interplay between interspecies encounters among people and cephalopods and the gradual revision of ethical obligations toward nonhuman animals more generally.