They toil not-
"Denham's--"
Consider the lilies of the field, shut up, shut up.
"Dentifrice ! "
He tore the book open and flicked the pages and felt them as if he
were blind, he picked at the shape of the individual letters, not
blinking.
"Denham's. Spelled : D-E-N-"
They toil not, neither do they . . .
A fierce whisper of hot sand through empty sieve.
As Montag attempts to understand anything from the book he is reading (it may be the Bible, not sure), he is blasted with advertisement jingles. Like sand through a sieve, he can try to attempt to read it over and over again, but it does not seem like he is able to retain that information in his head. Similarly, this analogy could also apply to the emotion of the people in the society of F451: they need to continue consuming entertainment, as any time away from it would lead them to unhappiness, which as is apparent with Mildred, they can not stand without 'turning to mush.'