John Clare's "Mouse's Nest" is a fourteen line poem which depicts the nest of a mouse found by the speaker. The mouse's nest is a "ball of grass among the hay." This illustrates the idea that we (all living things) live within a natural world (the grass (our existence) within the hay (the world itself)).
At one point, the narrator wishes to see a bird emerge from the nest. Unhappily, the narrator sees a mother mouse (nursing her babies). The narrator is horrified and runs away. This speaks to both the beautiful and ugly (to some) things in nature. Not all of the creatures of earth possess beauty (or not all people understand beauty in the same way).
In the end of the poem, the mother mouse finds her moved nest. Her finding of her nest, her home, forces all things to stop for a moment (water could not run). Even the cesspools (typically thought to be disgusting) "glisten in the sun."
The natural world is illustrated in both negative and positive light (just as people see things--both negatively and positively). In some circumstances, while one sees ugliness in the world (the speaker and the mouse), others see beauty (the mouse and her home). This is the reality of the natural world.
In this sonnet Clare, a peasant's son who grew up close to the land, chronicles a simple event, revealing through his word choice a farm worker's realistic view of the land. The narrator pokes a ball of grass he sees amid the hay. He is experienced enough to know it is a nest, and he presumably hopes he can catch the bird inside it. Instead, a mouse runs out. The imagery is simple and down-to-earth, described in matter of fact way: the mouse is not personified or romanticized, though it does represent the the natural world. It "bolts" with "all its young ones hanging at its teats." The narrator doesn't find this a pretty picture, for he says the mouse looks "odd" and "grotesque." The mouse, showing a decided lack of maternal instinct, then hurries "from her crawling brood." The baby mice squeak, and the mother finds her nest again. The narrator walks on and sees "broad old cesspools" that "glitter" in the sun.
The images in the poem show the reality of nature on a farm: a grotesque mouse, squeaking baby mice, a cesspool. Nature is not terribly ugly--there is also wheat, grass and a trickle of water running over pebbles--but nature is not prettified or turned into the kind of idyllic scene an urban audience might dream of. The poem conveys that nature is what is and nothing more.