Why faces don't always tell the truth about feelings

Human faces pop up on a screen, hundreds of them, one after another. Some have their eyes stretched wide, others show lips clenched. Some have eyes squeezed shut, cheeks lifted and mouths agape. For each one, you must answer this simple question: is this the face of someone having an orgasm or experiencing sudden pain? Psychologist Rachael Jack and her colleagues recruited 80 people to take this test as part of a study1 in 2018.