What is the ratio of American casts on episode 2 of the series? Please include their roles.
American refers to birth_country = 'USA'; cast refers to category = 'Cast'; ratio = divide(count(person_id where birth_country = 'USA'), total(category)) where category = 'Cast'
SELECT CAST(SUM(CASE WHEN T2.category = 'Cast' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T2.category), T1.role FROM Award AS T1 INNER JOIN Credit AS T2 ON T1.episode_id = T2.episode_id INNER JOIN Episode AS T3 ON T2.episode_id = T3.episode_id INNER JOIN Person AS T4 ON T2.person_id = T4.person_id WHERE T3.episode = 2 AND T4.birth_country = 'USA'