Harris and Brando
I'm sure this has been widely noted before, but Harris' entire performance in this movie was an imitation of Brando! Most notable are the long moody stares and silent reactions (a la 'One the Waterfront') and the brutal flashes of anger, especially in the house (a la 'A Streetcar Named Desire'). Now I know Brando was a huge inspiration to many actors at the time and indeed still now - but Harris' performance was SO like Brando that I couldn't take it seriously. Especially as Brando was far more gifted an actor as Harris (no offence to any Harris fans out there).
I guess it's worth noted that Harris had worked with Brando the previous year in 'Mutiny on the Bounty', so I guess he tried to learn some tips!
Armstrong and Bain are the true legends