There was no rehearsal time built into the shooting schedule of Mystic River, so Sean Penn spearheaded his own series of impromptu readings. With Oscar wins for Penn and co-star Tim Robbins, as well as a nomination for Marcia Gay Harden, clearly it was time well spent. Watch below to hear what happened behind the scenes. And to see the final product, catch Mystic River, airing all month on AMC.