It's not like we're showing her masturbate just to have a masturbation scene.
The scene: Issa just casually wants to quench her thirst solo and is frustrated to find that the batteries in her vibrator are dead.
While the scene does not depict Sally masturbating on screen, it's implied and later confirmed by her mother, Betty's, reaction afterwards.
And CW shows don't typically show sex, let alone masturbation.
The scene: Keough's character, an escort, enjoys watching herself masturbate.
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I thought, most of the sexuality in the movie is not glamorized. I wanted to know what her desire looks like. It's showing every part of this person and her private moments. Her comments on it: "That was shitty. And after we filmed it, he was like, 'Okay. I don't care about masturbating on screen; I don't care about sex scenes on screen.