Emily Dickinson only titled one out of 1,789 poems she wrote, and this isn’t the one. Sometimes Dickinson poems are given numbers. Ralph Franklin, the Dickinson scholar of all Dickinson scholars, assigned this poem number 1,096. Still, there's not much that the number 1,096 can tell us about this poem.
For simplicity’s sake, then, let's go by the first line of the poem. “A narrow Fellow in the Grass” isn’t a bad title for this little guy, and we'd say it's a pretty effective first line, too. (The title it was first published under, “The Snake”—check out the story behind the publication in “In a Nutshell”—could have been thought up by a class of third-graders.) How is it so effective? Well, just think about the ways that it announces some core themes that will be developed in the poem.
Way #1: We learn of a "narrow Fellow." At first, the reader is put in mind of a person, not a snake. This sets us up for the (we think intentional) confusion between humans and animals that will continue throughout the poem.
Way #2: This "Fellow" is "in the Grass." Of course, that's a perfectly reasonable place for a snake to be, but it's also a good place for a snake to hide. What is hidden and what is revealed seems to be a key concern of this poem, what with its boy speaker and whip that becomes a snake.
Of course, the real intrigue of the poem (and why folks continue to write and think about it do this day) is what is never revealed to the reader. It's not one of those "here's-my-theme" poems that comes right out. Instead, like a snake in the grass, this poem seems narrow and simple at first, but then twists out of our grasp. And the first line goes a long way to set us up for that experience.