As Ralph approaches Castle Rock in the final chapter, he is crushed to find Samneric, the twins, guarding the area against him. They represented his final hope of building up an "outlaw tribe" on the other end of the island. When Ralph realizes that they have joined forces with Jack, his sense of defeat deepens. Still, he wants to reach out to the twins.

When Ralph approaches the twins, it's clear that they are only acting out of the orders they have been given. Sam tells Ralph to "shove off," but Ralph assures them that he's come to Castle Rock specifically to see the two of them. Together, the twins indicate that Jack and his tribe have hurt them in order to gain their alliance. Ralph wonders aloud what he has done to deserve such a fate, and the twins insist that he needs to go "for [his] own good." They tell Ralph that Jack hates him and that the entire group plans to hunt Ralph down the next day.

Ralph again begs Samneric to join him, telling them that the three of them would stand a decent chance against Jack's group. Sam replies that Roger is a "terror," and Eric adds that Jack is as well.

The twins refuse to join Ralph because they are operating from a place of self-preservation; since they are brothers, they also understand the importance of keeping family safe. It is clear that Jack and Roger have hurt Samneric enough that the boys believe that real harm will come to them if they align with Ralph, and they simply aren't willing to risk it.

In chapter 12, Ralph realizes he is alone and goes into hiding. Previously, he had counted Samneric as the last two boys loyal to him. After Piggy’s death, however, he is forced to reconsider this position. As he eavesdrops on the tribe dancing on Castle Rock, Ralph hears them shouting “Kill the beast!” Even in the darkness, he recognizes Samneric by their synchronized motions and realizes that they have become “savages like the rest.” Nevertheless, he takes one final chance to regain them as his allies and climbs up the rock to speak to them.

Both boys urge him to leave, explaining that the others hurt them to force them to change sides. Emphasizing the danger he is in, they tell him that the next day, he will become the prey of the tribe’s hunt, and they reveal the sound that they will use as a signal.

As it dawns on Ralph that this danger is real, he asks what the hunters will do to him. He pleads with the twins to join forces with him. They do not reply directly, but talk around the subject. Sam gives him a chunk of meat. As he begins his descent from the rock, he decides to risk confiding in them.

Ralph tells them that he plans to hide in the thicket and asks them to keep the others away. Again, Samneric do not answer directly, and they neither agree nor refuse his demand. Instead, he hears their “incomprehensible reply”:

Roger sharpened a stick at both ends.

Ralph then climbs down and hides in the thicket. The next day, he hears the signal and the boys approach. Samneric tell Jack that he is inside.

Ralph's conversation with Samneric after Jack has captured them and they become "part of the tribe" emphasizes the total devolution of society on the island. First Ralph tries to point out to the twins that they don't truly belong to Jack. He says, "You two aren't painted. How can you--? If it were light--" This fragmented argument is meant to arouse shame in the boys, but because it is dark, they do not keenly feel their guilt. When the twins admit they have been physically hurt in order to gain their compliance, Ralph asks, "Who? Jack?" Ralph continues to try to reason with the boys, asking, "What have I done? I liked him--and I wanted us to be rescued--"

The boys explain that "the chief" and Roger hate Ralph and that "they're going to do you." Ralph continues to try to understand why the boys hate him and to proclaim his innocence, but the twins realize that none of that matters anymore. Jack has made up his mind, and Jack and Roger are now "terrors." When the boys hear someone approaching, Ralph says, "I'll lie up close; in that thicket down there ... so keep them away from it. They'll never think to look so close." He then asks pleadingly, "I'm going to be all right, aren't I?" and then asks twice what the tribe plans to do when they catch Ralph. Samneric reply only, "Roger sharpened a stick at both ends." It turns out that Samneric are tortured and reveal what Ralph said about his hiding place, making Ralph's quest for survival even harder than if he had not confided in the twins.

Although Ralph has a hard time understanding what Roger's sharpening a stick at both ends means, it's clear that the tribe intends to hunt Ralph as if he were a pig, showing that their society has lost all moral grounding and is willing to commit savage murder for no cause other than hate. 

First, he feels frustration and anger, but quickly realizes that will do no good.  Then he tells the twins where he is going to hide with the implication that they will lead the hunters in a different direction.  Then, finally, he asks them what will  happen to him once he's found.  He goes from trying to talk them into helping him to acceptance of his fate.