Fahrenheit 451 quote

PLEASE ANSWER THESE QUESTIONS. THANKS IN ADVANCE.

Once as a child he had sat upon a yellow dune by the sea in the middle of
the blue and hot summer day, trying to fill a sieve with sand, because some
cruel cousin had said, “Fill a sieve and you’ll get a dime!” And the faster he
poured, the faster it sifted through with a hot whispering. His hands were
tired, the sand was boiling, the sieve was empty. Seated there in the midst
of July, without a sound, he felt the tears move down his cheeks.

Questions :
1. What is the significance of this memory as Montag sits on the train? (pp. 7475)
a. Think about what happens next in the story (pp. 7475)
2. What does the author mean by “the sand was boiling”?