As debuts go, Guillermo Arriaga‘s explosive screenplay for “Amores Perros” is hard to beat. “21 Grams,” his follow-up with director Alejandro Gonzalez Inarritu, provided more than enough emotional red meat for Benicio Del Toro and Naomi Watts to carve into Oscar nominations. For his next trick, Arriaga nabbed the prize for best screenplay at Cannes 2005 for “The Three Burials of Melquiades Estrada,” a modern Western about friendship, responsibility and the unintended effects of violence. “Babel,” which stars Brad Pitt and garnered the best director award for Inarritu this year at Cannes, opens in the fall. Michael Fox speaks with Arriaga for SF360.