Theme in Yellow
Since the poem is coming directly from the pumpkin-speaker, the overall sound has a similar conversational vibe to it. It's light, fun, and simple, but it also shares some qualities with similar kinds of ghost stories and fairy tales kids are likely to hear. For example, we get phrasing like this: "On the last of October" (6). Sounds kind of like a Grimm's tale or any other story kids might hear before bedtime.
But we do have some more poetic devices happening here as well, like the alliteration we hear in "terrible teeth" (13). The effect though is similar to what we hear in those fairy/folk tales with the repetition of that toothy T sound that accents the appearance of those terrible teeth, a la "Little Red Riding Hood." The sound of the tongue at the back of our teeth (where it has to go to make the T sound) reminds us of our teeth themselves. Neat, huh?
Notice, though, that this sound game doesn't go on too long, just for two words. It's as though the speaker didn't want to give too strong an impression. He's just joshing, after all. All in all "Theme in Yellow" is conversational and playful, and an important element of that play is the kind of sounds that it makes.