It's said all humans mysteriously lose 21 grams upon their death, a notion that inspires much hard-boiled philosophizing in Mexican director Alejandro Gonzalez Inarritu's structurally ambitious follow-up to Amores Perros. As in that film, several characters’ lives become intertwined via a tragic accident, but here told via a chronologically disjointed structure that's a masterfully wrought puzzle of editing and plot construction. Given that unusual structure, the musical soundtrack by Gustavo Santolalla by necessity carries much of the film's mood and emotional undercurrents in its spare, brooding cues and occasional songs. The composer's primary instruments here are a heavy-vibrato electric guitar (its tone reminiscent of the great Ry Cooder) and an equally altered accordion, set against a ambient wash of electronics and percussion that's so murky as to often seem impenetrable. The Kronos Quartet admirably matches the mood with their closing rendition of the haunting "When Our Wings Are Cut, Can We Still Fly." The hip-hop swing of Ozomati's "Cut Chemist Suite" and R&B of Ann Sexton help anchor it in a more familiar frame of reference, while Benicio del Toro's spooky, spoken-word take on "Shake, Rattle and Roll" (a performance recorded in Memphis' legendary Sun Studios, no less) effectively channels Tom Waits by way of David Lynch. Another fine example of the evocative, genre-free possibilities of modern film music. --Jerry McCulley