The lieutenant tested soldiers in visional training.
"Tell me, private Smith," he said, "how many men are there in that trench-digging group over there?"
"Thirty men and one officer," was the quick reply.
"Quite right," said the lieutenant, after a pause. "But how do you know one is an officer? They are very far from here."
"That's easy, sir. The officer is the only one who isn't working."