Perceiving, representing, and reasoning about the human body is an incredibly difficult task; the fact that we traffic in this ability with such ease is no mean feat. After all, bodies are more than complex objects. They are more than a collection of parts that co-articulate, more than things that can be acted on, more than entities that are in the world and of the world. Rather, bodies act on the world. Bodies, by definition, are bodies in action: limbs move, joints articulate, digits bend and curl. Critically, many of these actions convey meaning: they are about the world. And it is precisely this meaningfulness of the human body in relation to the world that makes the task of perceiving, representing and reasoning about the human body both so complex and so critical.

Among other things, understanding the human body is central to our everyday social reasoning and social interactions: we perceive the body to read the mind. Goals and intentions, in particular, while generated by the mind, are instantiated in bodily acts. An event in which an arm moves at a 45-degree trajectory, and a rate of 15 centimeters a second, culminating in contact with a wine glass, is more than the collection of its surface features. It signifies an actor’s goal (obtaining the wine glass), reveals the actor’s underlying intention (getting a drink of wine), and can be a window into the actor’s proclivities and dispositions (liking wine).