The poem recited by Mississippi is an actual poem called "El Dorado" by Edgar Allan Poe. ↑ ほー、ポー。imdbトリビアより。
Robert Mitchum's character was wounded and needed to use a crutch, but Mitchum would switch which arm he used with the crutch throughout shooting.
The continuity was so poor that Wayne (who actually worked continuity in silents while a star college football player, a method used by Hollywood fans to slip players some spending money)
had his character mention it in one of the last scenes. The director enjoyed it so much he left it in the movie. Robert Mitchum's own version of this story is that he objected but Hawks had him switch sides with the crutch based on what looked best in that scene.
When Hawks saw how bad it looked in the dailies, Mitchum suggested the additional dialogue between his character and Wayne's to cover the gaffe.