It’s a phrase that should resonate with any dog owner. “It all goes down the leash,” says a gunnery sergeant in a U.S. Marine Corps K-9 unit to a new recruit as she struggles to tame an ornery German shepherd in the film Megan Leavey (opening Friday [June 9] ).

As played by Kate Mara, Megan Leavey is a punchy misfit with anger issues. The dog, Rex, is only slightly less approachable. Eventually, of course, these two mavericks train each other.

“It’s definitely true,” Mara says, calling the Georgia Straight from Toronto. “I think it makes sense that they use that term a lot in the marine corps. I kind of experienced it one day on-set when we were shooting one of the war scenes. I’d never done anything like that before. I wanted to get it right. The dog’s leash is actually connected to your vest, so he’s not just connected to you mentally: he’s physically connected to you. So we were sitting on the side waiting for them to call action and I was feeling quite anxious, and he just nudged up against me and put his head on me, and I could tell he was calming me down. He could feel my anxiety. I felt instantly protected, in a way.”

In real life, Mara herself is the proud owner—no, wrong word, companion to two Boston terriers who share her home in Los Angeles. The New York–born actor and House of Cards star was raised on theatre and musicals like Oklahoma! and The Sound of Music, and she cites Sissy Spacek as an influence on her own move into film acting. With its training and combat scenes, and the heavy drama that ensues after she and Rex are ambushed by insurgents in Iraq, Megan Leavey represents a break from Mara’s usual kinds of roles. But she approves of the film’s message, noting that the real-life Leavey was “very involved with who was going to make it”.

Enter Gabriela Cowperthwaite, whose 2013 documentary Blackfish brought enormous attention to the debate around captive cetaceans. In her first narrative feature, Cowperthwaite tells the story of Leavey’s hard-fought campaign to allow war veterans to adopt their unit partners—a doubly poignant issue for the former marine and Rex after they were both traumatized by their experiences. If the film takes some heat for ignoring the context of an unforgivable military aggression, its heart is still in the right place if you’re a devout animal lover.

“Of course,” Mara says when asked if our respect for animal intelligence should extend beyond the domesticated. “Of course. To me it’s so obvious: there’s a life behind the eyes. That’s one of the reasons I’m a vegan, but I guess some people aren’t aware of that, or they haven’t been exposed to the fact that animals have a lot more going on than just being raised to be our food. I know not everybody is aware of it, but, yeah—I think it’s one of the reasons that our movie is important.”