By rights, an 87-minute filmed monologue should be as stimulating as watching paint dry. Ah, but when the monologist is the brilliant Spalding Gray, then the audience is in for a cerebral feast. Based on his one-man Broadway presentation, Swimming to Cambodia is a mesmerizing account of Gray's experiences while playing a small role in the 1984 film The Killing Fields. Gray's ramblings encompass such subject as Southeast Asian politics, the availability of sex and drugs in the Third World, and even a few choice observations about New York City. The monologist sits at a desk throughout, while director Jonathan Demme makes no effort to "cinematize" the material. Still, the film is a fascinating hour and a half, and few viewers will feel the impulse to walk out of the theatre or fast-forward the VCR. Swimming to Cambodia was followed by another Spalding Gray "talking theatre" piece, Monster in a Box.