"The Circus Animals' Desertion" reads like the clash that it is. As Yeats' poet/speaker moves from the themes of myth and heroism to more personal matters of the heart in his poetry, and those two themes duke it out in the poem, the sounds and rhythms change.
He's a man torn between the things that made him famous and what he has left. In many ways, the poem sounds neat, orderly, and old school. The first two lines of the first section, for example, are in nearly perfect iambic pentameter. This is traditional poetry, with a capital P.
There's just one problem. Those traditional poems about myths and heroes just can't cut it anymore. And as our speaker/poet (cough Yeats cough) looks back on his past with dissatisfaction, the poem starts to sound messier and messier. The rhythms are off, and so are the sounds. The third line of the first section, for example, takes iambic pentameter and turns it all wonky:
Maybe at last, being but a broken man
This means that a poem that could have sounded like a stock and standard rhyme instead sounds a little different, a little… off.
Slant rhymes help to create this effect, too. Just take a look at line 13 in the second section. It ends on "destroy," but that's supposed to rhyme with "play" from line 9 and "away" from line 11. We've got a rhyming hiccup here.
In fact, this whole poem sounds just a bit off kilter. It's written in a strict form, but it never sounds stately or sing-songy. Don't get us wrong – it still sounds quite a bit like the high heroics of a good ol' epic – but at the end, there's that dull twinge of reality catching up with him.
It lobs us some weird sounds and unpredictable rhythms, and those wonky sounds help us feel just like the speaker does: that the rug has been pulled out from our feet, that our ladder has been taken away, that we're not sure where to go and what to do, because we're stuck between the old and the new.