Totally Starstruck
When Lenny Montana (Brasi) showed up on set, he was so overly nervous to act alongside Marlon Brando. In fact, he was so flabbergasted that he completely forgot his lines! Instead of getting upset, Coppola loved the nervousness as he felt that it fit with Brasi's character.
The Most Violent Scene
Sonny's death is easily the most violent scene in the film. He was ambushed, trapped, and shot in a scene that's been recreated thousands of times. To make this scene as immersive as possible, actor James Caan had to wear over 100 explosive charges all over his body. Then, when the time came, the film crew had to detonate the mini explosives to make it look like he was being shot.