IRMA P HALL does a straightfaced job as the strait-laced Mrs Munson, the Margaret Dumont to Hanks's Groucho. JK Simmons and Tzi Ma, as, respectively, Garth Pancake, the explosives expert, and The General (an enigmatic Vietnamese tunneller), are never less than kinetic irruptions of screwball, but it is Marlon Waylans, of Scary Movie infamy, who steals the picture as the inside man, Gawain.