That event gave him a new idea, and the following evening he made a groundwork of branches in the corner of the corral itself, and put down his blankets on the evergreens. Diablo was much concerned and walked about examining the new work from every angle. There Bull slept, and the next night he found that during the day the stallion had torn the boughs to pieces and scattered them about. He patiently laid a new foundation, and after this the bed was left strictly alone. In the meantime Bull had made a light, strong halter of rawhide, and after several attempts he managed to slip it onto the head of Diablo. Once in place, it was easy to teach Diablo that he must follow when he felt a pull on the halter--the first steps were rewarded with dried prunes, and after that it was simple. On that evening, also, Bull made his next step forward toward the most difficult proposition of all--he took a partly filled barley sack and put it on the back of Diablo. The next moment the sack was shot into the air as Diablo leaped up and arched his back like a cat at the height of his leap. He came down trembling and snorting, but Bull picked up the fallen sack and allowed him to smell it. Diablo found that the smell was good and that the hateful sack even contained things very good to eat. The next time the sack was put on his back he quivered and shrank, but he did not buck it off. After that, Bull spent his evenings in gradually increasing the weight of that sack until a full hundred pounds caused Diablo no worry whatever, and when this point had been attained, Bull decided that he might venture his own bulk on the back of Diablo. He confided his purpose to Tod, and the boy, greatly excited, hid himself at a distance to watch. In the beginning it was deceptively easy. Diablo stood perfectly unconcerned as Bull raised himself on the bars of the fence. And when the long legs of Bull were passed over his back, Diablo merely turned his head and sniffed the shoe tentatively. Slowly, very softly, steadying himself on the top bar of the fence, Bull lowered his weight more and more until the whole burden was on the back of the stallion--and then he took his hands from the top rail. But the moment he released that grip there was a change in Diablo, as though he realized that the man had suddenly trusted himself entirely to his mount. Bull felt a sudden wincing of all that great body; the quarters sank and trembled. He thought at first that it was because the horse was failing under the weight of this ponderous burden; but instinct told him a moment later that it was fear, and a mixture of suspicious anger.