Twentieth Century Fox has acknowledged that its decision to preview the Tom Cruise/Cameron Diaz comedy thriller Knight and Day last Saturday and at midnight screenings last night was aimed at offsetting negative tracking with positive word-of-mouth. "The best tool we had was the movie itself," Fox distribution chief Bruce Snyder told today's (Wednesday) Daily Variety. The trade publication said that Saturday's preview in about 500 theaters averaged 85-percent capacity. The film will be competing beginning on Friday with Sony's Grown Ups , starring Adam Sandler, Kevin James, Chris Rock, David Spade and Rob Schneider.