"Look, Scarlett is a gorgeous, gorgeous woman, but if you just compare purely physical features, plenty of girls are just as gorgeous," he explains. "But she creates this extra something. It's in her walk, her eye contact. The total package is just off the charts," Gordon-Levitt told Men's Health.
The actor had only Johansson, 28, in mind for his directorial debut and says he could not imagine the film without her.
"I didn't know Scarlett, but I spent more than a year with the image of her in my head playing this character. She couldn't not do this," the 32-year-old star said.