In Belgium we were told that the arrangement of the arms of windmills gave away the location of our troops.

At any rate everyone had a bad attack of spy-fever, and I did not escape it.

One night about half past ten I was going down a dark road to get my letters from the post office, when an officer on a bicycle came up to me and, dismounting, asked me where a certain British Artillery Brigade was.

I was not concerned with the number of the brigade, but I was horrified to hear the officer pronounce his "rs" in the back of his throat.

Of course, when we are not at war with Germany, a man may pronounce his "rs" however he pleases, but when we are at war with the great guttural hordes of Teutons it is different.
The moment I heard the sepulchral "r" I said, "This man is a German".
He told me he had come from the Indian Army and had a message for the artillery brigade.