Anthony Quinn was very disappointed when Marlon Brando was cast as Emiliano Zapata - he thought that with his Latin appearance, he would have been a better choice. To solve the argument, both actors competed to see which of them could urinate furthest into the Rio Grande. Quinn lost the bet, but he won an Oscar for the best supporting actor as Zapata's brother.
Marlon Brando was reportedly involved in a string of stunts during filming. On location in Texas, he shot off a string of firecrackers in a hotel lobby, serenaded Jean Peters from a treetop at three in the morning, horrified cast and crew by playing dead for several minutes following the hail of gunfire that ends Zapata's life, and told visiting reporters that he once ate grasshoppers and gazelle eyes.
According to Elia Kazan's autobiography "A Life" (1988), John Steinbeck would whittle while they sat in the wood shop of Steinbeck's New York townhouse writing the script. The two developed a deep and enduring friendship during the project.
Anthony Quinn had played Stanley Kowalski in the road tour of Tennessee Williams' play "A Streetcar Named Desire", and some critics thought he was better than Marlon Brando, who had originated the part. None of this was lost on Elia Kazan, who liked to foster competition between his actors if it was appropriate. On set, the competitive Quinn and Brando, who both liked and respected each other, bonded like the brothers they played. Ironically, Kazan had initially proposed Jack Palance, whom he had introduced in his earlier Panic in the Streets (1950), for the role of Zapata. Fox studio head Darryl F. Zanuck countered by offering Palance the role of Zapara's brother. The unhappy Palance then negotiated himself out of his Fox contract. Ironically, Palance had understudied Quinn in the road company version of "Streetcar," and when he was nominated for an Oscar for his role in Sudden Fear (1952), he was beaten by Quinn in "Zapata."