Final answer:
In 'The Black Snake,' Mary Oliver uses the phrase 'brighter fire' to metaphorically describe the black snake's speed, symbolizing the abruptness of life's end.
Step-by-step explanation:
In the poem "The Black Snake," Mary Oliver refers to the "brighter fire" as the black snake's speed. This comparison evokes the suddenness of death and the preciousness of life. The snake is not literally on fire, nor is it scared or representing its spirit in this context. Instead, Oliver uses this metaphor to illustrate the snake's vivacity and the swift, bright flash of its existence, which is abruptly ended by a vehicle. This portrayal aligns with her themes of nature's beauty and the tragic, often unnoticed, death of its creatures.