The film follows Bullock as a mom who is willing to do whatever it takes to protect her children from a mysterious force that has decimated the population, which kills anyone who looks at it.
Danielle Macdonald, who plays expectant mom Olympia in the film, told PEOPLE that while Bullock's character is understandably anxious throughout most of the movie, on set, the Oscar winner created a relaxed atmosphere that Macdonald especially appreciated.
"I'm quite emotional in most of my scenes, so it was nice to have that kind of reprieve and downtime on set," she said. "Getting in that mindset of crying all day, you tend to get a headache."
The Australian actress also praised Bullock for helping those involved on the film be able to relax despite the intense scenes they were filming.
"Sandy is this super cool person who manages to keep a funny, positive vibe on set even when you're doing heavy content matter," she said. "She's a really good connector of people. Sandy's just the life of the party. She loops everyone in and makes you feel really comfortable really quickly."
Part of the film takes place in a house, with a group of strangers banding together in an attempt to survive, and Macdonald shared that filming those scenes also helped her bond with her fellow cast members.
"These explosive strangers from completely different backgrounds, different ages and everything, they come together in this house to ward off this unseen threat," the 27-year-old explained. "It's so much about keeping everyone alive and that family connection that ends up being created, and really doing anything to the people that you love. It was really cool to find that family connection with each other."
As for Macdonald, she liked to unwind from her emotional scenes by hanging out with friends in Los Angeles, where the movie was filmed.
"When I would get off set, I would meet up with my friends or I would go cuddle with my animals," she shared. "Maybe watch some cheesy, fun show or movie, or something like that just to get me in a good headspace. Then the next day, get back into it."
Bird Box has been earning praise from celebrities including Stephen King and Chrissy Teigen, the latter of whom tweeted that the film had given her nightmares.
absolutely had the worst dreams of my life. john died, became a bird, called me on a tiny cell phone as a bird, I took a carry on to the Maldives with bird-john in it, was served strawberry cat on the flight. Woke up crying covered in sweat. bird box got me fucked up— christine teigen (@chrissyteigen) December 27, 2018
Photo Credit: Getty / Michael Tran