How do we know what another person is feeling? How can we tell that our friend is happy about her birthday present? How do we know our sister is sad at the family celebration? We may be able to tell because our friend is smiling when handed the present and because our sister is crying at the family gathering. But what if our friend was only smiling to be polite? What if our sister was crying at a wedding, would we still think she was sad, or could the opposite be the case? Th