Pain and shouting?

I was getting into my car today, and as I got into the driver’s seat I, the door started to close and I smacked my head against the top the of the car door (don’t ask me how I managed this). My ear took most of the force, and it stung like a mother for a good 30 seconds. Because I was on my own, I was able to shut the door and shout “AAAAAARGH!” loudly, followed by much cursing. This seemed to help. Why does shouting seem to help when we experience sudden intense pain?

You don’t have to scream and curse, as the following has shown:
“Fiddle-dee-dee, that will require a tetanus shot!”

-Homer Simpson

It’s an entirely cultural phenomena. An old National Geographic did a report on an indigenous tribe in South America that had a healer who would perform bush style trephinations (a medical procedure where a small hole is cut into the skull to allow for the release of cranial pressure). Each person who was operated on was not anesthetized and was fully awake but no one screamed in pain or cried. When asked if the procedure was painful they all responded that it was the most painful thing they had experienced, but the concept of crying and shouting when in pain was totally alien to them.

Can anyone back this up? It sounds like complete bunk to me, and the behaviour of very small babies when they hurt themselves seems an ample rebuttal.