CREATE TABLE table_67635 ("Prod. No." TEXT, "Title" TEXT, "Written by" TEXT, "Directed by" TEXT, "Original airdate" TEXT)

Who directed the episode written by Dan Serafin and aired on July 23, 2008?
SELECT "Directed by" FROM table_67635 WHERE "Written by" = 'dan serafin' AND "Original airdate" = 'july 23, 2008'
SELECT "Directed by" FROM "table_67635" WHERE "Original airdate" = 'july 23, 2008' AND "Written by" = 'dan serafin'