Chiwetel Ejiofor in “Backrooms.”

The new cerebral horror film “Backrooms” cleaned up at the box office this weekend, bringing in $81 million domestically and $118 million total including worldwide sales. Thousands of people have found themselves lost down the rabbit hole of the chilling movie, which happens to take place nearly entirely in a Bay Area strip mall.

The film opened with the largest box office haul ever for an original horror movie film and eclipsed distributor A24’s previous biggest hit (“Civil War”) by $55 million. The unlikeliness of its success is compounded by the fact that it was directed by Kane Parsons, a 20-year-old YouTube filmmaking........

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