“By the time we break for lunch, my arms throb from holding up the gun and my fingers are hard to straighten. I massage then on the way to the dining hall.
The mood this quote suggests is exhausted. She says her arms “throb”. This is a word with very strong connotation of exhaustion. Saying her fingers are “hard to straighten” means she has been using them a lot and she must be exhausted. Saying she has to “massage” them suffers the same. So, the theme and mood of this quote is exhausted.