91. We can see in the human face what correspondence is like. In a face that has not been taught to dissimulate, all the affections of the mind manifest themselves visibly in a natural form, as though in their very imprint, which is why we refer to the face as "the index of the mind." This is our spiritual world within our natural world. Similarly, elements of our understanding are manifest in our speech, and matters of our volition in our physical behavior. So things that occur in the body, whether in our faces or in our speech or in our behavior, are called correspondences.