Paul Newman was concerned about his accent, so he spent two weeks in Mexico with dialect coach Walon Green.
Paul Newman opposed sound looping the picture, stating it interfered with the actors' performances, so a small (for that time) chest microphone was developed that eliminated around eighty percent of dialog looping, and saved its associated post-production costs as well.
Paul Newman wore a prosthetic nose for his character, and MGM shipped two of them each day to the filming location.
Paul Newman wasn't keen to take the role, but when he heard that his old rival Marlon Brando had turned it down, he accepted the part.