Answer:
While Christopher is waiting to snoop around his father's room some more, he describes the falling rain as looking like white sparks because it is falling so hard, and it's sound like white noise.
Step-by-step explanation:
The book The Curious Incident of the Dog in the Night-Time is about an autistic boy called Christopher who likes to act as an amateur detective.
He accidentally finds a letter addressed to him in his father's room one day, and reading it makes him curious so he waits for an opportunity to snoop around in his father's room again for more letters.
He has to wait for six days before the opportunity comes, and while waiting on the sixth day it rains very hard and he sat and watched the rain falling.
He described the rain as sounding, "like white noise everywhere, which is like silence but not empty. I went upstairs and sat in my room and watched the water falling in the street. It was falling so hard that it looked like white sparks (and this is a simile, too, not a metaphor)."