The film immediately sparked a 'Bird Box challenge' where people (often children) would have to cross a distance while blindfolded, both indoors and outdoors. When videos started to appear on social media of people bumping into objects and hurting themselves this way, Netflix issued a statement to discourage viewers from taking this challenge.
The setting is in Northern California as several NorCal cities are mentioned (Sausalito, Santa Rosa, Sacramento and Stockton) and the river that Malorie and the children traverse is the Smith River in Del Norte County near the California/Oregon border. However, according to the San Francisco Chronicle, the house where the survivors take shelter is in Monrovia near Los Angeles, and most of the non-forest/river scenes were shot in LA as well.
Sarah Paulson and BD Wong have previously starred together in American Horror Story: Apocalypse (2018). Danielle Macdonald also appeared in an episode of "American Horror Story's" sixth season, and Rosa Salazar (Lucy) appeared in four episodes of the show's first season as one of the murdered nurses trapped in the house.
This is not Pruitt Taylor Vince's first appearance in a post-apocalyptic film. He previously played Otis on Ходячие мертвецы (2010). Interestingly his character's name in this film, Rick, is the name of the main character in The Walking Dead, Rick Grimes.
The trivia items below may give away important plot points.
In a December 21, 2018 interview with "Bloody Disgusting", it's mentioned that the producers wanted the creatures to appear at some point, and they even designed a creature and shot a scene with one. However, it made the scene funny, and for this it was discarded. Sandra Bullock described the creature saying "it was a green man with a horrific baby face".
At first, the title seems to refer to the shoe box where the children keep their birds, as an early warning system for when the creatures are near. However, the title may also refer to the building at the end where Malorie and the children take refuge, since it is has an enclosed courtyard filled with birds.