One of the fun things about dialectal differences in English is how the poetry turns out. There are some rhymes that just wouldn’t work in your own dialect of English, but work fine in another. For instance, the way I learned that Canadian English has a different pronunciation of sorry from mine was by hearing a Nickelback song on the radio five hundred million times in 2002:
“It’s not like you to say sorry
I was waiting on a different story.”
My hometown of Pittsburgh has this too, as I found out reading a poem about the game in which the Terrible Towel (the original rally towel, which Pittsburghers wave at Steeler games, Olympic award ceremonies, weddings, births, presidential inaugurations, etc.) debuted:
“‘It was easy,’ said Andy
And he flashed a crooked smile,
‘I was snapped on the fanny
By the Terrible Towel!'”
That probably seems like terrible poetry to you, not only because it is, but also because the bolded end-rhymes of the second and fourth lines aren’t remotely similar. But to native Pittsburghers, they are. That’s because we have two vowel shifts that move us away from the “standard” American English pronunciations. Both of them are “monophthongizations”, which is a really fun word to say once you figure how to. Monophthongization is the process of converting a diphthong to a monophthong (I’ll explain those terms in a minute.)
The first vowel shift is the conversion of /aɪ/ to /ɑ/ before an l or r. /aɪ/ is the phonetician’s way of writing what you learn in school as “long i”; it’s the vowel in sight, rhyme, or the pronoun I. It is a diphthong, which means that it’s really two vowels jammed together. If you say sight really slowly, you’ll notice that your lower jaw comes down as you start the vowel (the /a/ part), and then it starts back up, moving into sort of an “ee” sound (the /ɪ/ part) before you stop. If you don’t have anyone looking at you right now, try it yourself, and you’ll actually feel your mouth move from /a/ to /ɪ/. That’s a diphthong; it’s a sound where you start at one vowel and keep going until you finish at a new vowel. A monophthong, on the other hand, is a vowel sound that has the same sound throughout, like the /æ/ sound in American English hat. (Or the /a/ in British hat.) If you say hat slowly, you’ll notice that you start the vowel with your lower jaw down, and you only raise it back up when you start to make the t sound at the end, maintaining more or less the same vowel sound throughout. If you’re having trouble seeing the difference between mono- & diphthongs, don’t worry. The only crucial point is that the vowels in question are different in some way.
Returning to the Pittsburgh monophthongizations, we convert /aɪ/ to /ɑ/ before an l or r, so smile has a vowel that’s more like an “ah” sound than the standard “long i”.* The other monophthongization is the conversion of /aʊ/, the sound in Standard American English town, to /a/, another “ah”-type sound. This is why Pittsburghers sometimes write “dahntahn” for downtown. The first of these monophthongizations isn’t particularly rare in American English, occurring (if I remember correctly) in Appalachia, and parts of the Eastern Midwest as well. The second monophthongization is pretty much unique to Pittsburgh, at least among American English speakers.
And that’s how the rhyme works. /aɪ/ in smile turns into one “ah”-like vowel, and /aʊ/ in towel turns into another “ah”, and tah-dah! We get poetry that seems like free verse to anyone from another city! And at the low cost making the word pairs dowel-dial, foul-file, towel-tile, and vowel-vile more or less indistinguishable.
*: Since this shift only applies to vowels before an l or r, Pittsburghers pronounce the vowels in smile and smite differently.