CREATE TABLE table_31379 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( million ) " TEXT)

Who directed the episode that had 3.55 million viewers?
SELECT "Directed by" FROM table_31379 WHERE "U.S. viewers (million)" = '3.55'
SELECT "Directed by" FROM "table_31379" WHERE "U.S. viewers (million)" = '3.55'