An Avox is a citizen of Panem who has committed a heinous crime against the nation. They are taken to the Capitol where they are tortured, having their tongues mutilated, and forced into slavery serving the high class Capitol citizens. When Katniss first sees the Avox girl in the Capitol, she remembers the girl from when she is hunting in District Twelve. As Katniss is hunting, she recalls seeing a girl running from a capitol aircraft. Then the girl is caught, mutilated, and made a mute slave to the upper class.
Katniss feels sympathetic to the girl, who is now an Avox, and feels guilty that she stood by without helping her. The scene where Katniss remembers the girl sparks even more hatred towards the Capitol and Panem's government in Katniss' heart and mind. This hatred moves the story forward because Katniss becomes even more determined to survive the games. She is driven to win in order to invoke political change. This shows that Katniss despises the Capitol and all it stands for. It reinforces the theme that absolute power corrupts absolutely.