The Thing about Quatrains...
Yeah, this verse is about as free as it gets, but that doesn't mean it doesn't have any form at all. For one, throughout it uses the popular format of quatrains (four-lined stanzas). All kinds of poets seem to be fans of quatrains, so Williams isn't being too wild and crazy there. Choosing this standard format has the cool effect of taking the commonplace language and placing it in a poetic context. You know, by arranging these words like a poem, all of a sudden we can see the poetry in everyday language. Take the last stanza for example:
What are all those
fuzzy looking things out there?
Trees? Well, I'm tired
of them and rolled her head away. (37-40)
You could just easily write these same lines out as a couple regular prose-like sentences, but by arranging them in a quatrain the poet ask us look at them as poetry, not prose. It's like he's using this format to show us that there's deep beauty and meaning in the way we speak. This is especially true with this final stanza, where the plain language of the grandmother's words carries much meaning because they're the last words she'll ever speak.
Meter Chop Salad
Though there's anything even vaguely resembling a regular meter in this poem, that doesn't mean that there aren't very specific rhythms. The third stanza is a good example of the kind of tricks Williams is pulling.
Gimme something to eat—
They're starving me—
I'm all right—I won't go
to the hospital. No, no, no (9-12)
See how choppy the rhythm is? Read it out loud, and you can hear it. The dashes at the end of the first two lines put a bit of a longer pause before the next line comes. Then he throws a dash in the middle of the third line and a period in the fourth. Both of these are examples of caesura, which is just a fancy word for when a poet puts a pause in the middle of a line. After all this choppy pausiness, Williams then chooses to end the stanza with the repetition of "No, no, no" which speeds the rhythm up again.
Don't think that all this pausing and speeding up is just Williams being a slacker about his meter. Instead, it's him doing a sweet job of communicating the natural rhythms of a woman who's confused and panicked. If you want to get across the feeling of someone who's feeling erratic, why not use an erratic rhythm, right? Williams pull this trick for the entire poem, making the whole thing feel like a frantic, headlong rush to the grandmother's last words.