One striking finding in developmental and cognitive psychology is that people make rich inferences about the intentions and experiences of objects that look nothing like humans or animals. What makes these scenarios appear social, not just mechanical? Three studies explore this foundational level of social cognition: the detection of sentience. We probe inferences among what we posit to be core components of the concept of sentience—affect, autonomy, and perception—as well as physical markers of inanimacy. We find that children and adults share the belief that a fact about one of these three “sentient properties” implies the presence of others, to a moderate degree. Meanwhile, information about sentience blocks inferences of inanimacy. This link between sentience and animacy is particularly strong for US adults and White children, while people from other cultural backgrounds demonstrate a more flexible construal of what kinds of objects might be sentient.