How do the hunters damage the wall in "Mending Wall?"

In Robert Frost's poem "Mending Wall," the narrator is inspecting the stone wall on his property for damage. He writes that the hunters "have left not one stone on a stone," meaning that they have not simply piled one stone on top of another. Instead, to flush the rabbits out of their hiding places and "please the yelping dogs," the hunters have created gaps between places in the wall. No one hears the hunters making these types of gaps, but the narrator and his neighbor find them in the wall when they go to inspect it in the spring. The types of gaps the hunters make are very different than the effects of the natural swelling of the frozen ground, which makes boulders spill out of the top of the wall and makes very large gaps.