I'd love going to parties if I did this kind of research. What do you do for a living? I tickle rats. They seem to enjoy it. http://www.freesciencelectures.com/video/rats-laugh-when-you-tickle-them/ http://www.wnyc.org/shows/radiolab/episodes/2008/02/22 [Broken] Actually, the entire Radio Lab show about laughter is pretty interesting. The segment on laughing rats starts about 8 minutes in.