Ah, now it makes sense.
The trailer for the Denzel Washington-starring movie was released on Thursday (June 12), and features a slow building Em track as its background music. After Sia sings for about half a minute, Slim's emotive crooning comes in: "It's too late to start over," he belts, dragging out the final sound of that last word.
As Sia adds in lines like "Guts over fear," the snippet of the song suggests it will likely follow in the footsteps of Em's recent rap/pop motivational tracks, like "Not Afraid" and "Won't Back Down."
Eminem and Sia collaborated on "Beautiful Pain," off of The Marshall Mather LP 2 last year.
"The Equalizer" hits theaters in September.