Symbolism, Imagery, Allegory
Oscar: Not A Grouch
Junior's poor little dog Oscar is shot by his father in the book's tearjerker of a second chapter. Long story short: Junior's dad kills Oscar because he doesn't have enough money to pay a vet bill:
I ran away from there as fast as I could.
I wanted to run faster than the speed of sound, but nobody, no matter how much pain they're in, can run that fast. So I heard the boom of my father's rifle when he shot my best friend. (2.59-2.60)
Yup: we're chopping onions over here. Don't mind us.
The death of the animal, who is a complete innocent, becomes a symbol for the senseless destruction caused by poverty on the reservation. In fact, Junior mentions Oscar's death as the worst thing about poverty: it's even worse than being hungry.
We see this developed in the deaths that follow Oscar: Arnold's grandmother, Eugene, and his sister Mary.