Let's say you are walking down the street with your friend, and neither of you is saying anything, and he stops mid-stride, looks down and slightly to the side, and then closes his eyes briefly as if in concentration. What is he doing? He could be trying to drive an unpleasant, troubling, or even devastating thought or memory from his mind. People often assume this posture when doing exactly that. Your poor friend! A pang of remorse? Our lives are so full of pain, emotional fixations plague us. How can we live? His mother's violent death, perhaps, remembered (upsetting) or fantasized about (disturbing). Or he could simply be engaging in a little surreptitious off-gassing (embarrassing, satisfying). The possibilities range from the sublime to the ridiculous (but which is which?), and they look basically the same. Here we have a key element in the difficulty of interpreting human behavior.