When a bird is taking center stage in a poem, you better perk up your ears. Not only is that little sucker singing all day and all night, but Dickinson is helping him make music with a host of sound effects in this poem. Let's tune in, shall we?
First up, we have some consonance to greet us as we first start the poem:
"Hope" is the thing with feathers -
That perches in the soul – (1-2)
If you stop to read those lines out loud, it might sound like you've got peanut butter stuck to the roof of your mouth. That's because the TH sounds in "thing," "feathers," and "That" work together to thicken the sound of these lines and bring them closer together in your mind's ear—if you can imagine that. We haven't gone two lines and already we see Dickinson using sound to tie her lines tightly together, almost in the same way that the speaker is showing us how hope is linked together with the human soul.
After these first lines, Dickinson's sound party is just getting started. Next up is alliteration, which comes at us in lines 3 ("without […] words"), 6 ("sore […] storm"), and 10 ("strangest Sea"). All of these repeated beginning sounds add a kind of bounce to the lines, much like our speaker's message of hope is meant to add a kind of bounce to a reader's spirits.
And it's probably not a coincidence that two of those alliterative phrases start with S. This poem is lousy with S sounds—they're all over the place. In fact, 14 different words in this short poem either start with S or feature an S sound somewhere. If you think about it, all those S's make a certain sense. This poem is meant to soothe the senses of those sensitive souls searching for solace. The S sound is fundamentally a gentle balm, moving easily through the poem as the speaker reminds us to keep our chins up—hope will always be there for us. Sigh…