in social interactions, especially in eyes set in a smiling face, dilated pupils mean enjoyment and delight. Babies are highly sensitive to such cues—as are aphasiac adults (people who, usually due to a stroke, have lost the ability to understand spoken language). Because they pay heed to physical/emotional rather than verbal messages, young children and aphasiacs have a much better sense of when they are being lied to than most of us.
