The most interesting camouflage work was done for the benefit of snipers or for observers at listening-posts close to the enemy trenches. It was very important to spy on the enemy and discover his plans, and so men were sent out as near his lines as possible, to listen to the conversation and to note any signs of unusual activity which would be likely to precede a raid. These men were supplied with telephone wires which they dragged over No Man's Land, and by which they could communicate their discoveries to headquarters. Some very ingenious listening-posts were established. In one case a papier-mâché duplicate of a dead horse was made, which was an exact facsimile of an animal that had been shot and lay between the two lines. One night, the carcass of the horse was removed and the papier-mâché replica took its place. In the latter a man was stationed with telephone connection back to his own lines. Here he had an excellent chance to watch the enemy. On another occasion a standing tree, whose branches had been shot away, was carefully photographed and an exact copy of it made, but with a chamber inside in which an observer could be concealed. One night while the noise of the workmen was drowned by heavy cannonading, this tree was removed and its facsimile was set up instead, and it remained for many a day before the enemy discovered that it was a fake tree-trunk. It provided a tall observation post from which an observer could direct the fire of his own artillery. FOOLING THE WATCHERS IN THE SKY In the early stages of the war, it seemed impossible to hide anything from the Germans. They had eyes everywhere and were able to anticipate everything the Allies did. But the spies that infested the sky were the worst handicap. Even when the Allies gained control of the air, the control was more or less nominal because every now and then an enemy observer would slip over or under the patrolling aëroplanes and make photographs of the Allies' lines. The photographs were carefully compared with others previously taken, that the slightest change in detail might be discovered. Airplane observers not only would be ready to drop bombs on any suspicious object or upon masses of troops moving along the roads, but would telephone back to their artillery to direct its fire upon these targets. Of course, the enemy knew where the roads were located and a careful watch was kept of them.