The youngster had apparently lobbed his shoe at the jeep - with a M2 heavy machine gun post on the back - as it drove past in a convoy of other vehicles.
A soldier operating the weapon suddenly ducked, raised it on its pivot then pressed his thumb on the trigger.
That's from a chilling account of the second incident in Fallujah, from Britain's Mirror; two civilians died. The Mirror's reporter says he was "six feet from the vehicle when the first shots rang out, without warning." Read it, by all means.
(Thanks to TBOGG.)