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.