On the treadmill today I was listening to last week’s All Songs Considered episode about odd musical pairings. Aretha Franklin and George Michael make an appearance, singing “I Knew You Were Waiting.” I was delighted to hear Eddie Vedder and Nusrat Fateh Ali Khan’s “The Face of Love,” I’ve been a longtime fan of that one. Frank Sinatra and Bono’s rendition of “I’ve Got You Under My Skin” got, um, under my skin, in the worst way.

But clearly the entire time I was stewing over what song I’d nominate. The answer that came to mind isn’t really a pairing, it’s just one song sampling another – Mariah Carey’s “The Roof,” based on Mobb Deep’s “Shook Ones, Pt. II.” It’s not even Mariah Carey’s first rap pairing – for her prior album, she’d memorably recruited Wu-Tang’s Ol’ Dirty Bastard (may he rest in peace) to ride shotgun on the delightful pop romp “Fantasy.” But I’d still go with it.

I consider the song itself quite an underrated confection. Mariah had clearly taken to heart critical murmurings that her inevitable ascent into whistle register during her songs was an annoying crutch, a circus trick. So for the album on which “The Roof” appears (1997’s Butterfly), she toned it down. Her highest notes are mostly absent, barely detectable in the texture of the occasional harmony. And in fact, the album’s second number-one single, the Spanish-guitar-inflected “My All,” showcases her smoky lower register. (It’s hard not to hear “My All” as an answer to Toni Braxton’s “Unbreak My Heart,” another sultry, Spanish-guitar-filled, deep alto ballad with a very similar melodic structure.)

In “The Roof,” Mariah’s formerly unrestrained melisma just slinks and teases and flirts in the shadows, while a dozen Mariah clones harmonize lushly in sung whispers and sighs. Even in the background, her trills and coos are so delightfully precise that it’s amazing to think this is her holding back. Sometimes she’s just humming melismatically. And the production is top-notch – matching the vocal coquetry with barely audible strings and the hint of a triangle throughout that finally just takes over. It reminded me of something Sasha Frere-Jones once wrote about a Beyonce b-side: “Who feels comfortable with adding so much unexpected, generous harmony to a trifle about a delicious crush?”

The song, as I mentioned, builds off a sample by the gangsta rap crew Mobb Deep – a foreboding arpeggio picked out haltingly on piano keys atop a thrumming, bouncing bass line. The Mobb Deep song is an urban gothic nightmare – all the guns and money and swagger you’d expect, but instead of the usual threats or boasts, it foregrounds the fear itself. Shook – as in “scared to death, scared to look.”

So it’s an odd pairing – this scary Mobb Deep joint with a bit of sexy Mariah Carey cotton candy. It either loses or gains a bit of its oddness, though, when you consider the context.

Butterfly was a pivotal album for Mariah. It came right after she’d broken with her career-enabling ex-husband, Sony’s Tommy Mottola, whom she’d later complain had locked her into a cloying, sugar-pop chastity belt of a public image that obscured the R&B diva within. Fast-forward to today, when she’s perceived as having successfully reinvented herself in the contemporary R&B tradition. To me, contemporary Mariah is about as vocally remarkable as, oh, say, Ashanti (remember her?), but who am I to start railing about kids these days?

Until Butterfly, all we’d ever really seen of Mariah was hints of belly button. But “Honey,” the album’s first video, has her diving into a swimming pool in a bikini and stilettos. And suddenly, she’s an R&B queen! There she is on “Breakdown,” going toe to toe with Bone Thugs ‘N Harmony! (Another candidate for oddest pairing, but again I say – pop romp.) To complete this transition, to move fully from “virgin” to “urban,” she needs cred. She’s gotta go deep. Mobb Deep. Hence, “The Roof.”

And I love it.