Today, Nature carries this article about new research from Prof Richard Wiseman. From the article:
“New research has revealed that the red nose and face-painting traditionally associated with clowns may have its origins in science.
Psychologist Richard Wiseman of the University of Hertfordshire in the United Kingdom used highly sensitive infrared imagers to observe people as they laughed at jokes and video clips. The devices were able to accurately map heat changes in the face.”
The image below, from the research, shows the effect: