CREATE TABLE table_3451 ("No. in series" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( million ) " TEXT)

Who directed the episode that had 12.88 million viewers?
SELECT "Directed by" FROM table_3451 WHERE "U.S. viewers (million)" = '12.88'
SELECT "Directed by" FROM "table_3451" WHERE "U.S. viewers (million)" = '12.88'