Why does Katniss break glimmers fingers with a rock?

Why does Katniss break glimmers fingers with a rock? she has to use a rock to break it from glimmers fingers. she is loosing her mind and everything is spinning but she keeps going. she uses the hover craft coming to retrieve a dead body, so she lays on glimmers body to shield the bow.

she has to use a rock to break it from glimmers fingers. she is loosing her mind and everything is spinning but she keeps going. she uses the hover craft coming to retrieve a dead body, so she lays on glimmers body to shield the bow.