Why Sandra Bullock Had 'A Lot of Hard, Sad Days' While Filming Netflix Thriller 'Bird Box'

Just because Sandra Bullock is beaming about her newly released Netflix thriller, "Bird Box," doesn't mean the Oscar winner didn't have "a lot of hard, sad days [on set]."

The film -- which follows a blindfolded woman (Bullock) desperately trying to save herself and her children from coming face to face with a mysterious force that decimates whatever it touches -- made Bullock think about "things that no one wants to think about."

The mother of two opened up to PEOPLE about the difficulties of playing a role that forced her to put herself through emotional anguish.

"It was a lot of hard, sad days [on set]," she told the publication. "There was a day that I had to do this speech about [Sarah Paulson], and we were in the house, and you just have to get to the place of, 'I'm going to have to start thinking about things that no one wants to think about.'"

"But that's what the movie's about -- what is my greatest fear?" Bullock added of the apocalyptic film, in which she and Paulson play sisters. "I had to think about it all the time."

Bullock's greatest fear, she said, is "being away from my children." She explained that her life has been enriched in ways she could have never imagined since adopting daughter Laila, 6, and son Louis, 8, who she welcomed just months after she split from ex-husband Jesse James.

"We're very lucky that we get to live in this moment in time where we get to choose what our family looks like, and I got to do that in real life," she said of her two black children.

"You imagine so many things for yourself, but when it appears, it's better than anything you could ever imagine," she continued. "And in ['Bird Box'], it is about family, in a sense, in that 'sight' has us choosing things based on a preconceived notion of what that image must be like, when in fact it's the exact opposite."

"And here are these people who have that taken away, and you are actually given the family that is going to take the best care of you, that wants to take care of you, that wants to be there for you -- and how that that looks is very different from what most people expect," Bullock added. "But I think what I loved about this is that it sort of mirrored what I feel about real life, in that my family is not how most people thought it would look, but it's better."

"Bird Box" is now available to stream on Netflix.

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