 Why did Alan jump towards the robot when it fell into the mud?
The robots were built to serve Man; to do his work, see to his comforts, make smooth his way. Frowning, worrying about the sounds, Alan momentarily forgot to watch his step until his foot suddenly plunged into an ant hill, throwing him to the jungle floor. He tried to run, but vines blocked his way and woody shrubs caught at his legs, tripping him and holding him back. Without pausing to think, Alan leaped back, and fell sprawling over a bush just as one of the robots rolled silently up from the right, lowering its blaster barrel to aim directly at his head. With an awkward jerk the robot swung around and fired its blaster, completely dissolving the lower half of the cat creature which had clung across the barrel. But the back pressure of the cat's body overloaded the discharge circuits. The robot started to shake, then clicked sharply as an overload relay snapped and shorted the blaster cells. The metal killers, tuned to blast any living flesh, would murder them the instant they stepped from the ship! In the movement, his elbow struck the top of a small earthy mound and he was instantly engulfed in a swarm of locust-like insects that beat disgustingly against his eyes and mouth. Then, like an ambient fungus, it slithered off into the jungle undergrowth. The planet's double moon had risen and he could see a robot rolling slowly across the clearing in his general direction, blasting indiscriminately at whatever mind impulses came within its pickup range, birds, insects, anything. Apparently the robot hadn't sensed him yet, but Alan didn't know what the effective range of its pickup devices was. Minutes later, looking back he saw that the machine, though several hundred yards away, had altered its course and was now headed directly for him. He thought of a brown-haired girl crowding with the others to the gangway, eager to embrace the new planet, and the next instant a charred nothing, unrecognizable, the victim of a design error or a misplaced wire in a machine. Powerful as a small tank, the killer robot was equipped to crush, slash, and burn its way through undergrowth. Nevertheless, it was slowed by the larger trees and the thick, clinging vines, and Alan found that he could manage to keep ahead of it, barely out of blaster range. The twin moons cast pale, deceptive shadows that wavered and danced across the jungle floor, hiding debris that tripped him and often sent him sprawling into the dark.
 He saw a chance to exploit a weakness of the robot's.
 He thought the mud would protect him from the fire caused by the blasters.  He saw a chance to exploit a weakness of the robot's.  He knew he would not survive the attack and wanted to take the robot down with him.  The robot would not be able to see him he was right on it.