The vivid imagery of the first stanza can also be interpreted as a series of metaphors that Hughes is using to describe his daughter Frieda listening intently to the night. As she tunes her ears to her surroundings, she becomes:
A spider's web, tense for the dew's touch.
A pail lifted, still and brimming—mirror
To tempt a first star to a tremor.
There’s a tension between stillness and trembling in these images that captures Frieda’s sheer sensitivity to her surroundings. As a spider’s web, she’s “tense”; as a lifted pail, she’s “still.” But there’s also a “tremor” in these images, a faint trembling. Readers can imagine Hughes holding Frieda on his hip, feeling her at once perfectly still and quivering with tense alertness.
Both of these metaphors also suggest that Frieda is trying to capture something. The vision of the spider’s web waiting for the dew invites readers to picture a spiderweb hung with jewel-like drops, suggesting that Frieda is waiting receptively for something beautiful to arrive. But this metaphor also can’t help but raise the prospect of fly-catching—an idea that suggests Frieda might be hungry for what she hears and sees.
Meanwhile, the image of Frieda as a full and brimming pail stacks a metaphor on a metaphor. This imagined pail becomes a “mirror” trying to “tempt a first star to a tremor”—in other words, to capture a star’s reflection on its quivering surface. Frieda, then, is trying to take the world in, to make it a part of her. (The personification of the “tense” spider’s web and the “tempt[ing]” mirror strengthen that sense of hunger and fascination.)
This pair of metaphors further suggests that Frieda is already absorbing the world like a little sponge. A real-life spider’s web collecting dew and a brimming bucket might easily appear in the garden where Hughes and Frieda stand together. These metaphors show how deeply connected Frieda is to the scene around her.
The metaphors of the second stanza, meanwhile, tell readers something about Hughes’s imaginative experience of the night:
Cows are going home in the lane there, looping the hedges with their warm wreaths of breath—
A dark river of blood, many boulders,
Balancing unspilled milk.
In this moment, the gentle countryside sight of cows going home for the night becomes a grand, dark vision somewhere between a pagan sacrifice and a biblical plague. The cattle seem almost to be decorating the hedgerows for a ritual with their “warm wreaths of breath.” The conjunction of cows on parade and wreaths might even bring up echoes of Keats’s famous "Ode on a Grecian Urn," in which a “heifer” adorned in flowery “garlands” “low[s] at the skies” on the way to the altar: there’s a hint of ceremonious sacrifice here.
That hint gets stronger when Hughes describes the lane down which the cows walk as a “dark river of blood” full of “many boulders.” The cows here seem to be sunk in gore. But this startling image also introduces a mood of earthy fertility. The boulder-like cows, Hughes imagines, are “balancing unspilled milk”—and the milk and blood together might make readers think of birth as much as death. Blood and milk, after all, are what nourish a baby, first in the womb and then in the world. Here, Hughes might be seeing the astonishing fact of little Frieda’s not-so-long-ago birth reflected in the world around him.