"Arthur," I said, "you are not handsome, but you have sterling qualities and know a thing or two."

"You are not exactly a mezzotint yourself," Arthur retorted, "and I'm not sure that you have any particular qualities yet. What does this lead up to?"

"This," I said. "Suppose you are a sentry, outside barracks or an encampment of some kind."

"I'm supposing," he said.

"And suppose," I went on, "you don't know me."

"I've supposed worse things than that," said Arthur with decision.

"And try further," I said, "to imagine that it's a dark night, and I come along and don't notice you. You'd say, 'Halt, who goes there?' wouldn't you?"

"I should if I remembered my lines, I suppose."

"Very well," I said. "Then I should say, 'Friend.'"

"Well," said Arthur, "where's the catch?"

"There isn't a catch," I said. "What I want to know is, how do we go on after that?"

"I should ask you if you'd got such a thing as a cigarette about you," said Arthur.

"You might do that," I said, "but doesn't sound helpful. The reason I ask is because I've read the instructions several times in the papers on the courtesies to be observed when meeting a sentry; but the scene always ends at this point—'Friend.’ What happens next?"

"Perhaps the right thing," said Arthur, "would be for you to ask after the Colonel's wife. But I might not let you get as far as that. The odds would be in favour of my not believing you when you said 'Friend,' and in that case I should either shoot or pink you. The choice between these two processes would lie with me."

"But wouldn't that be rather sudden? Surely you make another remark first. I seem to remember something about 'sign and countersign.'"

"You're thinking of trigonometry, aren't you?" said Arthur.

"Perhaps I am," I said. "Anyway it's awkward not knowing what happens next."

"I know the best way to find out," said Arthur suddenly. "Get your boots on. We'll go and enlist."