Presently the road ends and the long sap begins.  You plunge into the dark winding alley much as into some old city’s ugly by-lane.  It is Centennial Avenue.  There is room in it to pass another man even when he is carrying a shoulderful of timber.  But you must be careful when you do pass him, or one of you will find yourself waist deep in mud.  I have said before that you do not walk on the bottom of the trench as you did in Gallipoli, but on a narrow wooden causeway not unlike the bridge on which ducks wander down from the henhouse to the yard—­colloquially known as the “duck-boards.”  The days have probably passed when a man could be drowned in the mud of a communication trench.  But it is always unpleasant to step off the duck-boards in wet weather.  Seeing that the enemy may have fixed rifles trained on you at any bend of the trench, it is unwise to carry a light; and in a dark night and an unaccustomed trench you are almost sure to flounder.

A party of men loaded with new duck-boards is blocked ahead of you.  As you stand there talking to another wayfarer and waiting for the unknown obstacle to move, a bullet flicks off the parapet a few feet away.  It was at least a foot above the man’s head and was clearly fired from some rifle laid on the trench during the daytime.  Every now and then the parapet on one side becomes dense black against a dazzling white sky, and the trench wall on the other side becomes a glaring white background on which the shadow of your own head and shoulders sail slowly past you in inky black silhouette.  The sharp-cut shadow gradually rises up the white trench wall, and all is black again until the enemy throws another flare.

As you talk there comes suddenly over the flats on your left a brilliant yellow flicker and a musical whine:  “Whine—­bang, whine—­bang, whine—­bang, whine—­bang,” just like that spoken very quickly.

“That’s right over the working party in Westminster Abbey,” says the last man in the procession.  “Some bally fool lit a pipe, I suppose.”

The man next him reckons it was about Lower George Street that got it that time.  “They been registerin’ that place all day on an’ off,” he says.

There was just that one swift salvo, and nothing more.  Presently, when the procession moved on, we came across men who had a shower of earth thrown down their backs by the burst of those shells.  Just one isolated salvo in the night on one particular spot.  Goodness knows what the Germans saw or thought they saw.  No one was hit, nothing was interfered with.  But it is a great mistake to think it all foolishness.  The most methodical soldier in the world is behind those other sandbags, and he doesn’t do things without reason.

Farther on we came through a series of hovels, more like dog kennels than the shelters of men, to the dark parapet where men are always watching, watching, across a hundred yards or so of green pasture, the dark mud parapet on the other side.  Here and there over a dug-out there fidgets a tiny toy aeroplane such as children make, or a miniature windmill.  The aeroplane propeller is revolving slowly, tail away from the enemy, clicking and rattling as it turns.  “Just-a-perfect-night-for-gas”—­that is what the aeroplane propeller is saying.