From the movie's first frames --- with children racing through alleyways, knocking over merchants and pottery, police kicking loose clay roof tiles, disrupted birds fluttering from gutters -- we hear the sound of their commotion made manifest in "O... Saya." It's a rumbling hybrid of Bollywood and hip-hop, a brand new collaboration between Rahman and M.I.A. It's the kind of cinematic moment where image and sound coexist. And that's only the first five minutes.

Filmed in the streets and slums of Mumbai, India, Boyle needed just the right music to compliment the film's cinema verité urban realism. He turned to internationally renowned composer A.R. Rahman (a huge star in South Asia--selling more than 100 million albums worldwide and 200 million cassettes--Rahman is one of the world's top 25 all-time top selling recording artists.) The film's score is central to the propulsive modern grit that pervades the story, but is also a nod to classic Bollywood productions where the music is front and center. And loud. Says Rahman, "We wanted it edgy, upfront. Danny wanted it loud."

M.I.A.'s appreciation for Bollywood music led her to record much of last year's Kala inside A.R. Rahman's studio in India, although the two had never worked together until now. Referring to him in URB magazine as "the Indian Timbaland," M.I.A. obviously jumped at the chance to work on "O... Saya" with the famed composer. Rahman says, "She's a real powerhouse. Somebody played me her CD and I thought, `Who is this girl? She came here and knew all my work, had followed my work for ages. I said, `Cut the crap, this "my idol" crap. You have to teach me.'"

M.I.A. crops up again, later in the film, with the remix of her worldwide hit "Paper Planes" seemingly made for Slumdog, as the lyrics pronounce, "Sometimes I feel like sitting on trains..." while a light blue locomotive chugs and hurls its way through India, young boys perched up top in the sepia sunlight scoping out for a scrap of food.

Other songs on the soundtrack include "Gangsta Blues," featuring hip-hop artist BlaaZe, which flutters with the rhythms of a film projector, capturing a bit of the madness of crowds as they disperse in a thousand directions to escape the claustrophobia of back alleys. And nothing quite prepares you for the triumphant climax, the overarching ode to joy that is "Jai Ho," closing out the film in a rousing sing-a-long that's had film audiences burst into spontaneous applause. As Rahman told Variety, "The energy of the film takes you through a roller coaster, and that's one of the main inspirations for the whole music."