In the poem "A Theory of Prosody," the speaker is actually talking about poetry and how it might be written. Prosody is how poetry sounds: the patterns, rhythm, and meter. This particular poem is written in a trimeter (three poetic "feet" which can be an iamb or a trochee). However, the rhythm depends on the reading/reader. Since the lines run on to one another (called "enjambment"), the rhythm seems suspended between the reader's inclination to pause at the end of each line and yet continue without pausing because the thought goes on to the next line. Therefore, this is in trimeter but could also be considered "free verse" if we ignore the pause at the end of each line.
So, the speaker decides that he will end a poetic line, regardless of when a pause should occur, when the cat draws blood:
time she drew blood I learned
it was poetic to end
a line anywhere to keep her
Levine's/the speaker's idea here is that the poetic line should end when something emotionally or physically affects him (that it should end when the line "draws blood"). Therefore, this "theory of prosody" is that prosody should not dictate how the poem's rhythm, meter, and structure should be. Rather, physical and/or mental affectation should regulate how a poem is made.
The cat is his muse, perhaps literally and metaphorically. At the end of the poem, the speaker suggests that (the cat now deceased) a poet should have some sense of a muse or an inspiration letting him know when and how a poem's real effects (drawing blood) build the structure of a poem.
This is the point of "A Theory of Prosody" and it is ironic only because the cat, at least in this poem, paws (pun on "pause") at regular intervals. However, it is not the regularity that structures the line breaks; it is the pawing and drawing blood. The flow and rhythm of a poem should be formed "anywhere" that it seems to have some significant effect.
Isn't that what it's about--
pretending there's an alert cat
who leaves nothing to chance.
The final lines of Levine's poem, ironically, if the first interpretation is true, seem to affirm the importance of prosody as a message of his playful verse; that is, that rhyme and meter, do, indeed, matter. For, such techniques as musicality, and a change in meter that "leave nothing to chance" can express better than words certain emotions. For instance, the use of ballad form by Robert Burns in his poems has long reminded his Scottish readers of the songs of their childhood, as well as of their distinct culture. This has endeared Burns's verse to them, while also touching their spirits.
In another example, one writer points to the poetry of Christina Rossetti as both connoting and denoting much with its prosody. Citing "Goblin Market" as an example, the writer demonstrates how Rossetti played with metric form, composing a poem which children could easily read because of this. While the words of the goblins sound like a chant--‘Come buy our orchard fruits,
Come buy, come buy--when the verse moves to the sisters in the poem, Laurie and Lizzie, the reader senses the contrast between these sisters and the goblins with the prosodic alteration. Thus, the meter and rhythm of this poem contribute greatly to its meaning as Rosseti, like the "alert cat," leaves "nothing to chance."