Explain Parker's analogy about crackers and how they compare to the Walkers.

Parker explains that if you shake a box of crackers through a sieve, only the crumbs and little pieces will fall through at the beginning, but that the whole crackers have to break a crumb at a time. In this analogy, he's saying that only the Walkers who have lost everything will receive tickets soon. Walkers like him who are still wanting to live are whole crackers who have to break apart before they "fall through the sieve."