A member of the Honor Guard of the United States Air Force must, at all times, maintain a somber and professional bearing. Airmen who wish to join must pass many tests to qualify to join the Honor Guard. Among them is the feared Rubber Chicken Test.
The airmen must remain rigidly at attention, unwavering, while instructors honk a rubber chicken in front of their faces. The chicken talks to them. But the airmen must never, ever waver. They must never smile. They must stare ahead, unmoved by the rubber chicken.
-via Ace of Spades HQ
I think we're so used to safety, that we think of ceremonial guards more as a show for the tourists, what with the colourful uniforms. And I bet the Sergeant-at-Arms never thought he'd ever have to fire his weapon again, but it's a good thing he was prepared. The world is getting a little stranger every day.
Last year, one was shot in the back in Ottawa at the National War Memorial. His murderer then forced his way into the Parliament building and was shot to death by the Sergeant-at-Arms (another "ceremonial" position).
http://en.wikipedia.org/wiki/2014_shootings_at_Parliament_Hill,_Ottawa