As soon as I saw Angela's Eyes I thought that it was based on the (ghostwritten) Robert Ludlum novel "The Ambler Warning". Both characters pick up on small facial and/or body movements that are too quick or small for most people to notice, these and other indicators such as voice enable them to tell when someone is lying or telling the truth. As readers of the book will know, there is a method by which they can be fooled, for the rest of you, there is a clue in this sentence.