The character Flowerchild (Maya Hawke), who is shown having cold feet on going through with the murders, and who flees the scene in the 1959 Ford Galaxie, is based on Linda Kasabian, who became a witness for the prosecution in the murder trial of Tex Watson, Patricia Krenwinkel, and Susan Atkins. In real life Kasabian was ordered by Tex Watson to wait in the car, during which she heard the murders inside the Tate residence take place and witnessed the murder of Wojciech Frykowski outside the house. Kasabian claimed she wanted to drive away, but was too scared.
Very rare for a Quentin Tarantino film, some scenes contained improvisation, particularly when Rick Dalton forgets his lines when filming a "Lancer" and afterwards rants to himself privately in his trailer. Leonardo DiCaprio had a very difficult time playing the scene as Dalton, rather than as how he himself would, especially since Dalton is supposed to be an actor of limited range. DiCaprio suggested that Dalton forget his lines mid-scene--ironically, to help him stay in character as Dalton. The subsequent scene in the trailer was also unscripted, improvised.
The producers had some initial difficulties convincing Hollywood Boulevard vendors to allow their premises to be fitted with period facades to better reflect the 1960s. However, after the production wrapped that section of the shoot, most of these same people asked if they could leave the facades in place, since they now much more preferred that period 'look.'
Donald "Shorty" Shea was a ranch hand employed by George Spahn. He had tried to warn Spahn about the dangerous nature of the Manson family. At some point he was jumped and then killed, with various body parts being buried around the ranch. One of the killers was Steve "Clem" Grogan - the hippie who knifes the tire and is confronted by Cliff. As he starts to change the tire you can see a cowboy in a corral in the background. As Shorty was the only ranch hand, this would have been him in the shot. His body was not found until 1977 when Clem agreed to show the police where the remains could be found.
When Sharon goes to a showing of her movie The Wrecking Crew (1968), the filmmakers chose to use the actual film rather than recreating the scenes with Robbie. The real Sharon Tate briefly appears on screen.
Quentin Tarantino: [female bare feet prominently featured in a shot] when Sharon Tate watches herself in the theatre, when Squeaky is watching TV at Spahn Ranch, and when Pussycat hitches a ride with Cliff.
Quentin Tarantino: [Mexican standoff] Many Tarantino films have featured Mexican standoffs (scenes where characters point guns at each other at the same time). This film has one too, but with a twist: Tex points his revolver at a stoned Cliff, who responds by making a mock gun with his hand and pointing it back at Tex.