Which original air date had 0.871 U.S. viewers (millions)?
CREATE TABLE "table1_26808178_3" (
  "series_num" real,
  "episode_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "u_s_viewers_millions" text
);
SELECT "original_air_date" FROM "table1_26808178_3" WHERE "u_s_viewers_millions"='0.871';