Abstract: Studies of human patients reveal dissociations between perception and action; some patients have implicit knowledge for a given domain, but can't access this knowledge for action. Studies of human infant development reveal a similar dissociation, suggesting that the neural systems connecting action with perception are not formed until the early preschool years, perhaps later. These connections are fundamental to our knowledge, to what we know about what we know. In this chapter I discuss the evolution of this knowledge, and argue that the dissociations seen in patients and in infant development are also seen in normal adult nonhuman primates, especially in the domain of folk physics. This suggests that for some domains of knowledge, animals don't know what they know. The disconnect between perception and action leads, in some cases, to perseverative errors. These errors, in turn, provide the signature of a highly encapsulated, modular system.