And Alcatraz knew, none so well! The deep exclamation of dismay from the rider was sweetest music to his malicious ears, and, in sheer joy of action, he rushed down the hollow at full speed, bucking "straight" and with never a trick attempted, but when the first ecstasy cleared from his brain he found that Perris was still with him, riding light as a creature of mist rather than a solid mass of bone and muscle--in place of jerking and straining and wrenching, in place of plying the quirt or clinging with the tearing spurs, he was riding "straight up" and obeying every rule of that unwritten code which prescribes the manner in which a gentleman cowpuncher shall combat with his horse for superiority. Again that thrill of terror of the unknown passed through the stallion; could this apparently weaponless enemy cling to him in spite of his best efforts? He would see, and that very shortly. Without going through the intermediate stages by which the usual educated bronco rises to a climax of his efforts, Alcatraz began at once that most dreaded of all forms of bucking--sun-fishing. The wooded hills were close now and the ground beneath him was firm underfoot assuring him full use of all his agility and strength. His motion was like that of a breaking comber. First he hurled himself into the air, then pitched sharply down and landed on one stiffened foreleg--the jar being followed by the deadly whiplash snap to the side as he slumped over. Then again driven into the air by the impulse of those powerful hind legs, he landed on the alternate foreleg and snapped his rider in the opposite direction--a blow on the base of the brain and another immediately following on the side. Underfed mustangs have killed men by this maneuver, repeated without end. Alcatraz was no starveling mongrel, but to the fierceness of a wild horse and the tireless durability of a mustang he united the subtlety which he had gained in his long battle with the Mexican and above all this, his was the pride of one who had already conquered man. His fierce assault began to produce results. He saw Red Perris sway drunkenly at every shock; his head seemed to swing on a pivot from side to side under that fearful jolting--his mouth was ajar, his eyes staring, a fearful mask of a face; yet he clung in place. When he was stunned, instinct still kept his feet in the stirrups and taught him to give lightly to every jar. He fought hard but in time even Red Perris must collapse. But could the attack be sustained indefinitely? Grim as were results of sun-fishing on the rider, they were hardly less vitiating for the horse. The forelegs of Alcatraz began to grow numb below the shoulder; his knees bowed and refused to give the shock its primal snap; to the very withers he was an increasing ache. He must vary the attack. As soon as that idea came, he reared and flung himself back to the earth.