How does Katniss know avox?
Avox is not actually a person. An avox is sort of like servant
to the citizens of the Capitol, except they usually have been
tortured and had something done to their tongues (the book doesn't
specify what) so that they cannot speak again. Katniss knows the
girl avox (as she is referred to) because when she was younger, she
and Gale were hunting when the giant Capitol hovercraft thing took
the avox out of the sky and into the hovercraft. Although not
stated in the book, you can assume she was then taken to the
Capitol, where she was tortured.