There is, however, a poem by Thomas Hardy called "The Darkling Thrush" that many fans have noted as having a thematic resonance with the film. The poem is not featured in the movie itself, but the themes of loss, hope, and the enduring spirit in the face of darkness present in the poem align with the film's narrative.
Here's a stanza from the poem:
"I leant upon a coppice gate
When Frost was spectre-grey,
And Winter's dregs made desolate
The weakening eye of day."
While this poem isn't explicitly used in the film, it's a testament to the power of art and how it can reflect and amplify the emotions and ideas present in other mediums.