The dampened smile

The dampened smile is an attempt to control an automatic, happy one and exists because some muscles, such as the ones controlling the mouth, are easier to suppress than others. “The cheeks will be raised but we pull the corners of the mouth downwards or press the lips together."

Not all cultures invite a broad smile.  In Japan, where etiquette dictates that emotions are stifled in public, there’s a greater emphasis on smiling with the eyes.