Get out the microscope, because we’re going through this poem line-by-line.
Lines 13-14
The fields quivering, the skyline a grimace,
At any second to bang and vanish with a flap;
- The wind is making the fields quiver and forcing the skyline to grimace (pull a strained face)—almost like it's bending the horizon of the world itself.
- The whole world seems like it might suddenly be blown away or just disappear, almost like a scroll suddenly rolling up, or a tent getting knocked over and blown away.
Lines 15-16
The wind flung a magpie away and a black-
Back gull bent like an iron bar slowly. The house
- These lines further highlight the violence of the wind. It's smacking birds around and bending them—ouch. In another simile, we learn that a black-back gull looks like an iron bar as it bends. It's like something strong getting forced into a shape by something stronger. The wind casually tosses both birds around.
- Hughes might be suggesting that the forces of nature are indifferent to life—either animal or human. These forces don't care what kind of damage they're causing. They're impersonal.