Katniss can see that the creatures are muttations. From a distance, they look like wolves but are able to balance on their hind legs. She follows Cato toward the Cornucopia and starts climbing, then remembers Peeta with his hurt leg. He lags behind and she shoots an arrow at one of the creatures. Peeta tells her to climb and she listens. Once at the top, she finds Cato struggling to recover, gagging over the side. Peeta still needs her help, so she shoots another of the creatures down, then helps Peeta up the Cornucopia's metal side. She can see that the creatures have razor-sharp claws and are able to spring high off the ground with their strong legs. There's something eerie about the creatures, something human, and Katniss soon realizes that they each represent one of the dead tributes, their fur color matching the tributes' hair, their eyes the very same, and the numbers around their necks corresponding to the districts from which they came. She's horrified to see the "Rue" muttation, the same dark hair and brown eyes, and wonders about their brains, whether they have any of the tributes' memories or they've been programmed only to hate those who have survived the Games so far.
The muttations continue leaping, and one is able to grab Peeta's leg. Katniss grabs his arm and is eventually able to pull him back up, but he's been bitten badly and is bleeding profusely. Then Cato recovers and gets Peeta in a headlock. Katniss can see that he wears a skin-tight mesh armor, but his head is exposed. Peeta, whose lips are turning blue, marks an "X" on Cato's hand in his own blood. Katniss shoots that "X", and Cato releases Peeta and falls from the Cornucopia. The muttations attack, but Cato's armor protects him for a while.
It is a long, cold night and, despite the tourniquet that Katniss fashions, Peeta is losing a lot of blood. Cato's moans are never-ending, and Katniss feels only pity for him and wants his suffering to stop. Morning finally comes and Katniss is able to see Cato below. Out of pity, she uses her last arrow to end Cato's life.
The cannon fires and the muttations retreat, but Peeta and Katniss must place distance between themselves and Cato's body before the hovercraft will come, so they move to the lake. Then, when it's just Katniss and Peeta left, Claudius Templesmith announces that the earlier revision to the Games' rules has been revoked, that only one Tribute can win.
Peeta pulls out his knife and Katniss instinctually points her arrow at his heart, but Peeta just tosses the knife into the lake. He tells her to kill him. Ashamed, Katniss refuses, deciding that to go back without Peeta would mean that a part of her would never escape the arena. She wants him to kill her instead.
She remembers the nightlock berries and offers them to Peeta, taking a handful herself. Peeta protests at first, but then she tells him to trust her and hopes that he understands. She says to hold the berries out because she wants everyone to see. She wants to make sure that the Gamemakers understand what she and Peeta are about to do and that if the Gamemakers allow this to happen, the Hunger Games will not have a victor this year. On the count of three, they pop the berries into their mouths. Immediately, Claudius' voice returns, frantically telling them to stop, that they are both winners in the Hunger Games.
The Gamemakers continue to manipulate the tributes, first by driving them to the Cornucopia and then by sending in their former opponents in the form of muttations. Not only did the Gamemakers possess the tributes as humans, but now they're using them as pieces in the Games even after their death. Katniss' friendship with Rue and her fondness of Thresh make these muttations particularly horrific for her.
The Games become so ugly, and the suffering so intense, that she can't bear even to hear Cato endure the muttations' attacks on his body. She knows, though, that this is exactly the entertainment that the audience wants: the pain and the gore.
Finally, when the Gamemakers revoke their original rule change that would have allowed two tributes to win, they reveal what has been their goal all along. They wanted the remaining tributes to be the star-crossed lovers so that the Games' final act would be the most dramatic: one lover killing the other. When Peeta raises his knife, the hunter in Katniss emerges; she aims an arrow at him before she realizes that he's tossing his knife into the lake. She's ashamed of herself, but she's a natural survivor, so her reaction is true to her character and true to the doubt that she has maintained about Peeta throughout the Games. Peeta, however, says that he wants Katniss to kill him, that he couldn't live without her. Katniss doesn't question him now, but she knows that she can't go back to District 12 without him. She refuses to let the Gamemakers have the final say, and when Peeta says that they have to have a victor, she knows that he's right. His statement, instead of causing her grief, gives her an idea.
Katniss' maneuver with the nightlock is her final and most significant act of defiance. The Games were all about controlling and manipulating the people of the districts, but by threatening to kill themselves with the poisonous berries, Katniss and Peeta force the Games to change, although the ultimate course of that change is left to the Capitol: Either Peeta and Katniss die and the 74th Hunger Games has no winner, or they reinstate the earlier rule and have two winners. Either way, Katniss — a girl from the districts — will succeed in rebelling against the Capitol by not giving it exactly what it wants.