It's been called one of the most revolutionary acts committed to film.
Forty-two years after the event it still packs a punch. Note that one of the main characters in this scene is an African-American and the other, an autocratic white plantation owner, looks like Dick Cheney.
In 1965, noted Mark Harris in 'Slate' magazine, in order to get the film made, "producer Walter Mirisch had to run the numbers and show United Artists that a picture in which Sidney Poitier one-upped a town full of white rubes could make money even if it never opened in a single Southern city."
Sidney Poitier plays the Philadelphia detective visiting a relative in the Deep South. He's arrested, vexatiously, by the local police. Beginning an almost routine process of trying to fix him up for a local murder, he reveals his identity. In a performance that won him an Oscar, Rod Steiger plays the role of Police Chief Bill Gilliespie. Initially an oafish redneck, the growing respect between himself and Poitier's Detective Virgil Tibbs is one of the great two-handers of cinema.
When production began in 1966, Poitier refused to shoot in the South. He was still traumatised by the experience of being tailed by Klansmen when visiting North Carolina with Harry Belafonte. Poitier reluctantly agreed to a few days of tense location work in Tennessee. Plagued by whooping rednecks, much like a scene from the film itself, Poitier told Jewison that he slept with a gun under his pillow. So it was in Illinois, not Mississippi, that the film was made.
The scene in question takes place in an orchid house attached to a grand mansion. Wealthy local Eric Endicott is being questioned about the murder by Detective Tibbs. He doesn't like it. He's not used to being talked back to by a black man. Tibbs speaks calmly, politely. Endicott lunges towards him, past a large white orchid in full bloom, and slaps him on his face for his insolence. Without warning, Tibbs slaps him back, harder. Endicott, astonished, nearly falls over. "There was a time,' he tells Tibbs, "when I could have had you shot." Tibbs, Gillespie and an astonished black servant bearing glasses of lemonade depart the room leaving Endicott to weep.
The slap wasn't scripted. No one knew Poitier was going to do it. And when he does it, you feel his reply to every policeman who ever harried him and every humiliation received over the years. The world changed with that one slap.