It has been suggested that the fixation of beliefs about people’s beliefs, desires and intentions is modularized. We argue that this is unlikely. We argue that there is modularity lower down: social-intentional ‘markers’ are produced by an encapsulated mechanism intermediate between perception and belief-fixation, and that these markers make a distinctive contribution to the fixation of beliefs about the mental. But belief fixation itself is not modular. Finally, we suggest some complications to our simple picture, and some ways in which our thesis might shed light on pathologies of social understanding.