What is the average height of a non-human superhero in Dark Horse Comics?
average = AVG(height_cm); non-human superhero refers to race <> 'Human'; Dark Horse Comics refers to publisher_name = 'Dark Horse Comics';
SELECT AVG(T1.height_cm) FROM superhero AS T1 INNER JOIN publisher AS T2 ON T1.publisher_id = T2.id INNER JOIN race AS T3 ON T1.race_id = T3.id WHERE T2.publisher_name = 'Dark Horse Comics' AND T3.race != 'Human'