A recent Freakonomics podcast/guest (Dr. Sapolsky) mentions that when you bite down softly on a wooden pencil, it makes eyes' crow-feet express, which artificia

A recent Freakonomics podcast/guest (Dr. Sapolsky) mentions that when you bite down softly on a wooden pencil, it makes eyes' crow-feet express, which artificially tricks your proprioception into thinking that you're smiling. This tactic can be used to with minimal conditioning/tolerance.