gelotology

Did you know that gelotology is the study of humor and laughter, its effects on the human body, and of medical abnormalities of laughing?
And did you there are two types of smiles? The Duchenne smile and the non-duchenne smile. THe duchenne smile basically means that your cheek muscles (zygomatic arch) are lifted and there is also a smile in/at your eyes (orbicularis oculi). Many researches agree that the Duchenne smiles indicate genuine spontaneous emotions since most people cannot voluntarily contract the outer portion of the orbicularis oculi muscle.

XD <-- Duchenne smile