The creatures chasing them are big old wolves that are clearly genetic "muttations" engineered by the Capitol (25.1).
Cato, Katniss, and Peeta all scramble for the safety of the Cornucopia. Cato reaches the top first, and then Katniss. Just as she's about to draw an arrow to shoot him she hears Peeta cry out with the mutts on his heels. She helps him climb to the top.
That's when Katniss gets a closer look at the pack of wolves: their eyes are strangely human. That's when she realizes that they ARE humans. The Capitol has somehow engineered the dead tributes into KILLER WOLVES.
Katniss fires into one of the wolves' (Glimmer's) throat. Then she recognizes Foxface, the boy from District 9, and worst of all, RUE. Peeta recognizes them too.
Peeta and Katniss fight off the pack, but then Cato (who had been recovering from being chased) comes up behind Peeta and gets him in a headlock.
Katniss doesn't know what to do. Her arrows are useless. Plus, if she shoots him, he'll take Peeta down with him into the pack of snarling wolves. Stalemate.
Peeta signals for Katniss to shoot Cato's hand, which she does, and Cato releases Peeta while he knocks Cato back into the wolf pack. Unfortunately, Cato doesn't die right away. He is being torn to bits by the wolves.
Still, though, no cannon. They can hear Cato slowly dying and moaning. What's worse is that Peeta is losing blood from his leg.
Katniss cuts off a sleeve from her shirt and makes a tourniquet for Peeta with her arrow. He may lose his leg, but it could also save his life.
Listening to Cato die is a nightmare and Katniss just wants his suffering to end. The Gamemakers won't put him out of his misery though, because "this is the final word in entertainment" (25.44).
Katniss makes Peeta stay awake through the night so he won't lose consciousness. Peeta tells her to shoot Cato with the arrow she used for his tourniquet. Katniss does and the cannon fires.
They did it! Yeah! But wait. Nothing happens.
They move down to the lake where the announcer's voice booms out that there has been YET ANOTHER change in the rules. That's right! Now there can only be ONE winner.
Katniss draws her arrow but can't kill Peeta. She won't let him kill himself. So what do they decide to do?
Katniss grabs the red poisonous berries that killed old Foxface. Peeta gets her idea, and they both take some in their hand. It's tragic lover suicide time! Peeta kisses her and then they start to pop them in their mouth.
Then suddenly, the voice of the announcer:
"Stop! Stop! Ladies and gentlemen, I am leased to present the victors of the Seventy-fourth Hunger Games, Katniss Everdeen and Peeta Mellark!" (25.94).