Army reservist witnesses war crimes

Is there some expression about a horse's mouth that applies here?

Army reservist witnesses war crimes: "In one government class for seniors, Delgado presented graphic images, his own photos of a soldier playing with a skull, the charred remains of children, kids riddled with bullets, a soldier from his unit scooping out the brains of a prisoner. Some students were squeamish, like myself, and turned their heads. Others rubbed tears from their eyes. But at the end of the question period, many expressed appreciation for opening a subject that is almost taboo. "If you are old enough to go to war," Delgado said, "you are old enough to know what really goes on." It is a rare moment when American students, who play video war games more than baseball, are exposed to the realities of occupation. Delgado does not name names. Nor does he want to denigrate soldiers or undermine morale. He seeks to be a conscience for the military, and he wants Americans to take ownership of the war in all its tragic totality."