Who wrote the episode with 3.92 million US viewers?
CREATE TABLE "table1_25740548_3" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "written_by" FROM "table1_25740548_3" WHERE "u_s_viewers_million"='3.92';