Here and there a house had been left intact, with its furniture untouched. It was not until later that it struck us as peculiar that these houses had been spared from the general destruction. Two or three days later, however, after we had moved in, and headquarters had been established, we discovered that under many of these houses, and at certain crossroads which had not been blown up in the usual manner, the Boche had left mines, timed to go off at any time up to twenty-eight days. One could never be sure that the ground underneath one's feet would not blow up at any moment. These mines were small boxes of high explosive, inside of which was a little metal tube with trigger and detonator attached. Inside the tube was a powerful acid, which, when it had eaten its way through, set free the trigger and exploded the charge. The length of time it took for the mine to explode was gauged by the strength or weakness of the acid in the tube. [Illustration: A TANK MOVING TO THE ATTACK DOWN WHAT WAS ONCE A MAIN STREET] We were also impressed with the mechanical genius of the German. The Boche had made a veritable mechanical toy out of nearly every house in the village which he had spared. Delightful little surprises had been prepared for us everywhere. Kick a harmless piece of wood, and in a few seconds a bomb exploded. Pick up a bit of string from the floor and another bomb went off. Soon we learned to be wary of the most innocent objects. Before touching anything we made elaborate preparations for our safety. One of the men was greatly annoyed by a wire which hung over his head when he was asleep, but he did not wish to remove it. He had decided that it was connected with some devilish device which would do him no good. Finally, one morning, he could endure this sword of Damocles no longer. With two boon companions, he carefully attached a string about fifteen yards long to the wire. They tiptoed gently out of the house to a discreet distance, and with a yell of triumph, the hero pulled the string,--and nothing happened!