Question: What is the average total gross for the movies featuring Sterling Holloway?
SQL: SELECT SUM(CAST(REPLACE(trim(T2.total_gross, '$'), ',', '') AS REAL)) / COUNT(T2.movie_title) FROM `voice-actors` AS T1 INNER JOIN movies_total_gross AS T2 ON T1.movie = T2.movie_title WHERE T1.`voice-actor` = 'Sterling Holloway'