In lines 1-5 of mending wall what do you think is the something that does not love a wall?

Mother Nature and Hunters

Lines 1-5 are:

"Something there is that doesn't love a wall,

That sends the frozen-ground-swell under it,

And spills the upper boulders in the sun;

And makes gaps even two can pass abreast.

The work of hunters is another thing:"

In these lines, it says that the something "that doesn't love a wall...send the frozen-ground-swell under it". This indicates that Mother Nature does not love a wall. She is the one that has the winter ground freeze and swell under the wall to make the boulders topple and fall away. The fifth line specifically says that hunters do not love a wall. They want to be able to chase game without any obstacles and walls are obstacles.