ET's Kevin Frazier hosted a Q&A at Los Angeles' Museum of Tolerance after a Selma screening, getting those involved with the making of the film to dish on the reaction to the movie.
"The energy that we're getting back from people, telling us their stories, telling us how they feel activated and energized by the story ... It's really unbelievable," director Ava DuVernay said.
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One of those stories of people who were involved in the historic event came from Tony Bennett, who joined the marchers and performed.
"I got a call from Harry Belafonte and he was the one that said to me, 'We're going to do a march in Selma for Martin Luther King, Jr. Would you come?'" Bennett told ET. "And when he told me what was going on with the blacks down there, I couldn't believe it, and I said to him, 'Okay, I'll go.'"
Bennett and Belafonte weren't the only celebs involved. Sammy Davis, Jr. and Joan Baez also stepped up for the cause.
Selma is up for four Golden Globes: Best Motion Picture, Drama; Best Director (Ava DuVernay); Best Actor in a Motion Picture, Drama (David Oyelowo) and Best Original Song (Common and John Legend for "Glory").
The biopic follows a crucial time in Dr. Martin Luther King, Jr.'s life when black marchers attempted to walk from Selma, Ala. to Montgomery in order to obtain voting rights in 1965. The journey took three attempts due to police resistance.
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Bennett recalled his performance for the marchers.
"It was a rainy night and we didn't have a stage so, of all things, they found a store of caskets and they actually built a stage with those caskets," Bennett said. "It was just one of those great nights."
Selma opens in limited release on Christmas Day. It goes wide Jan. 9.
Bennett's GRAMMY-nominated album with Lady Gaga, Cheek to Cheek, is available now. Bennett and Gaga will play at The Cosmopolitan in Las Vegas on Dec. 30.