Laughter brings out a red nose

http://www.nature.com/news/2008/080401/full/news.2008.715.html

A hearty laugh was associated with "both a reddening of the nose and a white
area directly around the mouth", says Wiseman. "These features form a key part
of the make-up traditionally associated with clowning, and could explain why
this unusual type of face-painting is associated with humour."