http://pagingdrgupta.blogs.cnn.com/2009/07/13/bleep-that-hurts/
“Thankfully, Dr. Richard Stephens and his team at Keele University in the United Kingdom just published a study that says swearing actually has a pain-lessening effect. (See Mom? It’s healthy!) When we swear, we increase our threshold for pain, meaning we can bear it longer and don’t feel it as much. Stephens is not sure why this happens, only that for some reason, ‘swearing appears to increase our pain tolerance.'”