Who directed the episode with 6.37 million viewers?
CREATE TABLE "table1_27927185_1" (
  "episode_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "originalairdate" text,
  "viewers_millions" text
);
SELECT "directed_by" FROM "table1_27927185_1" WHERE "viewers_millions"='6.37';