You are of course referring to the opening chapter of this classic dystopian novel that refers to Montag's penchant for fire and in particular the curious way that the books themselves are described as Montag and his colleagues burn them. Note how the books are given the qualities of living animals that are slaughtered:

...while the flapping, pigeon-winged books died on the porch and lawn of the house.

The books are given life, but this life is only to be extinguished when the firemen arrive and burn them. Likewise too when they raid the woman who burns herself and her book collection, this imagery is repeated as "books fell like slaughtered birds" and a book falls into Montag's hands:

A book lit, almost obediently, like a white pigeon, in his hands, wings fluttering. In the dim, wavering light, a page hung open and it was like a snowy feather, the words delicately painted thereon.

This imagery is used throughout the novel to make the crime of burning books and the destruction and loss of all the ideas, culture and thought that they represent worse. By depicting the books as birds, killing them is a much more heinous crime, as it helps us to see how books are not just inanimate objects but real life beings.