How many items are listed under the column of U.S. viewers for episode "Bite Me"?
CREATE TABLE "table1_21172539_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real,
  "u_s_viewers_millions" text
);
SELECT COUNT("u_s_viewers_millions") FROM "table1_21172539_1" WHERE "title"='\"Bite Me\"';