Regular rhyme scheme aside, Dickinson doesn't get too crazy with the sound games in this poem. (For more on the rhymes, check out "Form and Meter.") She does slip in some pretty slick assonance in the first stanza, though. Check out what she does with the long I-sound. We'll bold the places where the sound repeats, and you read it out-loud:
The Brain—is wider than the Sky—
For—put them side by side—
The one the other will contain
With ease—and You—beside—
(1-4)
So, even though all these other words with long I-sound necessarily fit into the rhyme scheme, Dickinson knits the opening stanza neatly together by weaving the sound through. She even gives us a near rhyme "wider" and an inner rhyme with the repetition of "side" in line 2.
We've got a couple other minor sound games in the poem as well. For example, "The Brain is deeper than the sea—" (5) hits us up with some more assonance, and "As Syllable from Sound" (12) caps the poem off with some good old fashioned alliteration.
So even though Dickinson doesn't get too elaborate with the sound games in this one, she definitely makes the poetic devices work for her, using them to weave together a cohesive and sonically pleasing poem. In other words, this poem feels whole and is just easy to listen to.