lion and the unicorn

"The study of pupil size as an indicator of emotion is known as pupillometrics. It was Eckhard Hess, a University of Chicago biopsychologist, who first used this term back in 1975. Hess has said he became interested in the study of pupils and dilation one night while in bed. He was looking through a book of 'strikingly beautiful' animal photos. His wife noted how big his pupils were and commented the light must be low, but Hess assured her there was plenty of light. The next day, he went to his lab and tested assistant James Polt with several photos of landscapes and one of a pin-up girl. Hess held the photos up to his head so he couldn’t see them, but noted that Polt’s pupils dilated when he saw the photo of the pin-up. The two embarked on their research on the subject after that."