Five-month-old infants know humans are solid, like inanimate objects.

Infants know that humans are exempt from some of the principles that govern the motion of inanimate objects: for instance, humans can be caused to move without being struck. In the current study, we report that infants nevertheless do apply some of the same principles to both humans and objects, where appropriate. Five-month-old infants expect humans, like all material objects, to be solid.