Dr. Paula Niedenthal and her colleagues argue that smiles are not simply the expression of an internal feeling. Smiles in fact are only the most visible part of an intimate melding between two minds. But most importantly, Dr. Niedenthal argues, people recognize smiles by mimicking them. When a smiling person locks eyes with another person, the viewer unknowingly mimics a smile as well. When they unconsciously mimic a false smile, they don’t experience the same brain activity as an authentic one. The mismatch lets them know something’s wrong.