"I know what you're thinking," we say, but how do we know what others are thinking or feeling? Because evolution has granted us what has come to be known as "Theory of Mind," the ability not only to be self-aware but aware of others' consciousness. Theory of Mind develops slowly-and in some cases, such as autism, develops little or not at all. Theory of Mind allows us to interact socially, to care about others, to manage our behavior in groups, to fall in love, and--less admirably--it allows us to lie.