This poem is really conversational. It sounds like you're just hanging out with a friend in a coffee shop, and he's telling you a story about the last words his grandma ever said. The poet includes slang and gives a choppy rhythm that reminds us the way real conversations go down. Check out the following stanza:
Gimme something to eat—
They're starving me—
I'm all right—I won't go
to the hospital. No, no, no (9-12)
So we've got the slang word "Gimme," which makes it feel way more conversational than any old school poem you've read (9). (Shakespearean sonnet, this is not.) We talk more about this in "Form and Meter," but notice how Williams uses dashes and that period in line 12 to create kind of an erratic rhythm. It gives us a real sense of the panic the grandmother must be feeling. It also reminds us of the way people talk about things in conversation sometimes—you know, like it's not always a well-crafted story. It comes in bursts of images since most memories are far from perfect.
We'd also be selling you short if we didn't point out the only rhyme in the poem. You probably already noticed the "go" at the end of line 11 and "No, no, no" at the end of 12. To us, this rhyme seriously accentuates the terror that the grandmother is feeling about going to the hospital. Later in the poem the grandmother cries, "Oh, oh, oh!" as the ambulance dudes are taking her away (21). This of course rhymes with and directly parallels the "No, no, no" from before (12). This repetition of sound kind of tracks the grandmother's progression from sickbed to the ambulance and highlights the fact that she's doing the exact thing she was so panicked about before. It's cool how Williams manages to make the poem sound like such a natural conversation, but at the same time carefully sculpts the language to draw our attention to certain things. Well, we think it's cool, anyway.