In the poem, the speaker describes a snake slithering through the grass - what is looks like, how it moves, and how it reacts to those around it. The speaker does not stop there, though - she also recalls her own experiences of stumbling upon snakes in the past and the emotions such experiences have given her.
The snake, who is the "narrow fellow in the grass," is described with various details. First, he appears as a "spotted shaft" riding through the grass and "divid(ing) (it) as with a comb"; he next "closes at your feet and opens further on" (Dickinson 5-8). The speaker also describes how the snake prefers "a boggy acre/A floor too cool for corn," where he can "(unbraid) in the sun" (9-10, 14).
Her own previous experience has proven that with snakes, their "notice sudden is" (4). They often seem to appear out of nowhere, creating a sense of shock, fear, and discomfort. As the speaker, a lover of nature and all kinds of creatures, states:
Several of nature's people
I know, and they know me;
I feel for them a transport
But never met this fellow,
Attended or alone,
Without a tighter breathing,
And zero at the bone (17-24).
Though she feels a sense of companionship, even comaraderie, with many of "nature's people," snakes leave her with a feeling of nervousness, tension, or even fear. And while, as a child, she sometimes tried to "(stoop) and secure" snakes she came across (15), they would quickly slither away, leaving her to realize they are not creatures to be tamed, but rather, perhaps, best avoided.