But don't worry--researchers are not recommending keeping a straight face to avoid low bone density. The healing and mood-elevating power of laughter is well known, as shown in a study reported last year by Psychiatric News. Patients with treatment-resistant obsessive-compulsive disorder were being implanted with a deep brain stimulation device when it was noticed that they began to smile or laugh. Researchers found that the more patients had laughed upon stimulation, the fewer symptoms they had two years later. For more information, see http://pn.psychiatryonline.org/content/45/11/16.2.