The "cry" of the hunter probably does not refer to their earlier chant. Throughout this whole chase scene the hunters are sort of yelling ("ululating"). I think they are doing it to be fierce and scary.

The rest of the lines you cite are going on in Ralph's head. He is being hunted and he is completely freaked out. He has hidden in some bushes but he is afraid that he will be found. That is why he is imagining that the savage can hear his heartbeat 15 yards away.

So he's freaking out, but he's also trying to psych himself up for what comes next. He's telling himself not to scream but instead to get ready for whatever happens next.