CREATE TABLE table_23958944_5 (no_by_season INT, us_viewers__in_millions_ VARCHAR)

What episode was watched by 10.81 million US viewers?
SELECT MIN(no_by_season) FROM table_23958944_5 WHERE us_viewers__in_millions_ = "10.81"
SELECT MIN("no_by_season") FROM "table_23958944_5" WHERE "10.81" = "us_viewers__in_millions_"