Sarah Pressman, [not pictured, see note 1 below] who is Professor of Psychological Science at the University of California, Irvine, and Principal Investigator of the Stress, Emotion & Physical Health Lab (STEP) has co-authored a recent paper which describes experiments aimed at reducing needle injection pain – by manipulating facial expressions.
“Expression was covertly manipulated via cover story and chopstick placement in the mouth.”
The experiments also investigated ‘grimacing’.
“Together, these findings indicate that both smiling and grimacing can improve subjective needle pain experiences, but Duchenne smiling may be better suited for blunting the stress-induced physiological responses of the body versus other facial expressions.”
See: Smile (or grimace) through the pain? The effects of experimentally manipulated facial expressions on needle-injection responses Emotion, Pressman, S. D., Acevedo, A. M., Hammond, K. V., & Kraft-Feil, T. L. (2020)
 The photo is from a previous study also involving chopstick smiles, and also co-authored by Professor Pressman : Contrasting Experimentally Device-Manipulated and Device-Free Smiles Front. Psychol., 15 October 2019.
 SmileSticks™ (an hygienic alternative to a chopstick, which were evaluated in the study above) can be purchased here
 The 2010 Ig Nobel Peace Prize was awarded to Richard Stephens, John Atkins, and Andrew Kingston of Keele University, UK, for confirming the widely held belief that swearing relieves pain.
Research research by Martin Gardiner