Rhythm
The poem doesn't bother with any standard form of steady meter. Makes sense to Shmoop. This poem is supposed to be about bucking the established structure, so why would Dickinson lock the words into a rigid format? The entire thing is more free-flowing than that. It punches where it wants to punch and chills where it wants to chill.
Check out the rhythm in the first two lines below. We'll bold the syllables that are stressed:
Much Madness is divinest Sense—
To a discerning Eye—
Much Sense—the starkest Madness— (1-3)
At first, it seems kind of all over the place, which makes sense for a poem that's talking about madness. The seemingly chaotic rhythm gives us a feeling that something wild is struggling to get loose. (Somebody better call the pound.) We would be leading you astray, though, if we told you that these words were just randomly thrown on the page.
Notice how lines 1 and 3 both begin with two stressed syllables: "Much Madness" and "Much Sense."
It's like the poem is sucker-punching us in the face. It's aggressively pointing out the main comparison that the poem sets up between supposed insanity and sensibleness. The rhythm grabs us from the get-go and makes no bones about letting us know what this poem is dissecting.
Rhyme
There's also no kind of regular rhyme scheme here, which makes the one rhyme in the whole thing really stick out. Check it:
Assent—and you are sane—
Demur—you're straightway dangerous—
And handled with a Chain—(6-8)
By only using rhyme in one place, Dickinson makes us sit up and pay attention to these two words. The rhyme smushes the words together in our minds, and we're reminded of how the speaker thinks that what regular people call sanity is a type of prison. On the purely technical tip, the rhyme puts a button on the poem, telling us, "Okay, this one's over. Move along."