Katie Aselton, Lake Bell, Kate Bosworth Get Gritty in 'Black Rock' (Video)

Director/star Aselton reveals what she cut from the film’s Sundance debut and her high and lowlights of filming the girl-centric thriller.

The story of Black Rock begins as a charming one.

Three childhood friends reunite to spend a no-frills weekend camping on an island off the coast of their Maine hometown. While relationships have been tested, and ultimately damaged, over the years, the girls attempt to reconcile while spending a few days away from their busy, adult lives. Until, that is, disaster strikes.

Turns out, Abby (Katie Aselton), Lou (Lake Bell) and Sarah (Kate Bosworth) aren’t the only ones on the island that weekend, and when things go awry, they must fight for their lives.

PHOTOS: The Scene at Sundance Film Festival 2012

“I had a blast doing this. I look back on this time and, without joking, it is one of my favorite things I’ve ever done,” Bell tells The Hollywood Reporter.

The off-camera story is equally charming. Aselton conceived the idea for the film alongside her filmmaker husband Mark Duplass, who wrote a first draft for the screenplay while on an airport layover. The low-budget thriller required a similarly no-frills approach to filming, and Aselton recruited actresses by asking herself, "who do I want to crawl through the mud with for a month?" From there, the trio lived together in a small house on the island and spent their days and nights in close quarters for a month of filming -- often covered in mud, blood and sometimes in the nude.

Drama hit behind the scenes, as well, when Bell suffered a “24-hour asthma attack” as a result of hypothermia from the frigid waters. “The water really is that cold,” says Aselton, describing the ordeal as her worst moment on set. The scene, in which Abby and Lou attempt to swim away from their attackers in the middle of the night, required little acting from Bell.

“That was all real,” she admits.

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Viewers got a first look at Aselton’s film at the Sundance Film Festival, where it premiered in January 2012. (See THR’s interview with the trio in Park City below.) But the version moviegoers will see beginning May 17 is a tamer, less gory one.

“The cut we went to Sundance with was much more over the top,” says Aselton, “and I just walked away from that with, ‘I’m just not comfortable with this. I want to simplify it and bring it back to my realm a little bit.’ And I’m OK if I don’t make all the genre people super happy with that. I need to be OK with it when I go to bed at night.”

Though billed as a horror film, Aselton and Bell agree that Black Rock is an “elevated” thriller.

“I like keeping it on an intellectual level,” says Aselton, but adds with a smile: “without sounding pretentious.”

Email: Sophie.Schillaci@THR.com; Twitter: @SophieSchillaci