 Why did Alan jump towards the robot when it fell into the mud?
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. 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. 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. Apparently the robot hadn't sensed him yet, but Alan didn't know what the effective range of its pickup devices was.
 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.