The fog gives Katniss burning stabs of pain wherever it touches her skin. Unable to stand the agonizing pain, they sprint away as fast as possible. Peeta is still slow to react after being hit with the force field, and Katniss briefly considers abandoning him, Finnick, and Mags and running to save herself. However, she immediately pushes it aside and puts all of her efforts into saving Peeta.
He is still holding up the efforts to run away from the fog, so Finnick carries Peeta and Katniss takes Mags. But the strenuous effort of running and the effects of the fog on her nerves make it impossible for Katniss to carry Mags. Finnick tells her he can't carry both Mags and Peeta, and he turns to Mags and apologizes.
Without saying a word, Mags grabs Finnick's face and kisses him on the lips before she runs straight into the fog. Moments later, the cannon blasts, signaling her death. Eventually, Katniss, Peeta, and Finnick make it to the beach. They use the salt water to release the fog's toxins from their body, and rest some more before they realize they are now surrounded by monkeys.
The monkeys lunge for them and they are able to defend themselves for a while, but the animals are becoming too many for them to handle. As Peeta is trying to hand his supply of arrows to Katniss, a monkey lunges for him. Katniss tries to throw herself in the path of the monkey, but she knows she'll miss. But suddenly another tribute, a drug addict from District 6, jumps in front of Peeta and the animal sinks its teeth into her chest.
Once again, Katniss resists the urge to leave Peeta, an urge the Capitol desperately wants her to give in to. She realizes that there are cameras recording their every move, and people will be watching to see how she reacts to the burning pain and the slow-moving Peeta. Katniss understands she can do what the Capitol wants her to and abandon Peeta, or she can stay to help him escape.
Katniss' decision to stay and help Peeta further reinforces the idea of rebellion. The Capitol wants her to forsake Peeta and prioritize her survival, instead of risking pain and death just to help him. That is how other tributes would act, and to work to save someone else would mean they're refusing to play the Quell the way the Capitol wants them to. When Katniss stays instead of running away, she gives more inspiration to the rebels. Her bravery and selfless acts will continue to fuel the growing dissent throughout Panem.
Another important element to note is the development of Finnick's alliance with Katniss and Peeta. Katniss is shocked and confused when Finnick chooses to carry Peeta and leave Mags to die. One tribute saving another instead of helping his district partner is unheard of. There was no hesitation on his or Mags' parts to save Peeta. This should deepen her trust of Finnick, and though she is grateful for his sacrifice, she is still confused.
Finnick's act of risking his life for Peeta is mirrored by the drug addict, the morphling from District 6. Katniss notices that she seems to come out of nowhere, and everything happens so fast she doesn't even have time to react. She has witnessed two other tributes save Peeta in quick succession and struggles to make sense of it.