In the third stanza of “Eating Poetry,” the mood shifts from unbridled elation to surreal unease. After the speaker happily devours pages of poetry and disappoints the librarian with his behavior, suddenly,

the poems are gone.
The light is dim.
The dogs are on the basement stairs and coming up.

The dimming light can represent a literal darkening as the library is being prepared to close at the end of the day. In fact, the poem ends with the library shut for the night in “the bookish dark.”

The light also can serve as a metaphor for joy and inspiration. Earlier, the speaker eagerly feasts on poetry—both physically and emotionally. He is so moved by the words that he feels compelled to absorb them as a reader and a diner. Nonetheless, when he finishes eating the poetry, “the poems are gone.” He uses up or consumes all of the poetry and is left without further food for thought or his stomach. The “light” he experiences—joy and inspiration—is “dim” without more poetry to feed on.

Finally, the dim lights mark a transition between a world of reality and a world of unreality and absurdity. Things become less clear and understandable in the darkened library. Why do dogs suddenly appear and enter the library? The fact that they emerge from a basement adds a sinister note—after all, why were they kept down in a presumably dark basement in the first place?

The speaker also transitions from an ordinary man into a dog, kneeling and licking the librarian’s hand.

I am a new man.
I snarl at her and bark.
I romp with joy in the bookish dark.

He is a both frightening (“snarl”) and playful (“romp with joy”). The poem ends with a bizarre, disturbing atmosphere of both menace and glee. Saying that “the light is dim” also combines the contrasting ideas of luminosity and darkness.