Brando, thankfully, had very little to do with the film, and it would have been significantly improved had someone else been cast in his role.
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Brando read his lines off of cue cards. and in some scenes I think he’s ridiculous with the cotton stuffed in his mouth. IIRC, Ernest Borgnine was considered for the role.
Brando makes the movie. Ernest Borgnine would have been a joke. One of the Oscars biggest mistakes was awarding him Best Actor for Marty, followed by Best Picture for Shakespeare in Love.