TORONTO -- With her new zombie film "Life After Beth," comedy star Aubrey Plaza was so excited to show more range than she gets to as deadpan April Ludgate on TV's "Parks and Recreation" that she over-exerted herself.

"I actually tore my abdominal wall or my abdominal muscles because they're very weak because I have no abs," she said, displaying her signature straight-faced humour in a recent interview. "I don't work on my abs. I need to do that."

Plaza plays the titular character, who dies but comes back to life as a zombie -- a state she doesn't initially realize she's in, and one which evolves slowly. John C. Reilly and Molly Shannon play her parents, who are so happy to have their little girl back that they don't let her in on the news that she's the undead. Dane DeHaan plays her boyfriend in the comedy that co-stars Anna Kendrick, Paul Reiser and Cheryl Hines.

Plaza said her injury happened during a scene in which she stands up with an oven/stove range strapped to her back along with a boombox playing smooth jazz -- methods her boyfriend employs in order to keep her calm and contained. The oven was hollow but "really heavy" and she got overzealous, said Plaza.

"I did like one crunch and I was like 'Ack!' So that sucked," she said. "But then afterwards they built this harness situation for the oven that kind of acted like it was a hiking backpack kind of thing with straps, and I was kind of strapped in and the weight equalized, so it was easier to carry after that.

"But the first day I just tried to pick it up on my own and I was like, 'I got this,' and then I didn't got it and it was a nightmare," she continued, adding jokingly: "I went to the doctor later. When we were shooting, you know, you just have to shoot, and Jeff (Baena, the writer-director) is a tyrant. I mean, he didn't care, he didn't want to hear it.

"He was like, 'Get that thing on your back and get your ass up. You need to do this four more times."'

Baena, who is dating Plaza and co-wrote the 2004 film "I Heart Huckabees," said he started penning "Life After Beth" in 2003.

He's always loved zombie films, but he prefers "the dead zombies as opposed to the virus zombies." And he wanted to make his zombies sentient and nostalgic for their old lives because it added "psychological trauma" and made it more "heartbreaking."

Like the brain eaters in the film, Baena thought the script was "dead" after years of sitting on the shelf, but it was resurrected when Plaza's agent told her about it. She and Baena, who live in Los Angeles, don't like to talk shop when they're together and she didn't even know about the project until then.

When she read it, she told him: "We have to do this tomorrow. This has to happen."

"It's kind of a slow burn and you don't really see that in a lot of zombie movies," said Plaza. "And also, most zombie movies are impersonal. They're kind of more apocalyptic and about big themes, higher concepts, fighting groups of people, survival. But this is like a really, really personal account of one family's story of a zombie takeover.

"It is interesting, if you watch other zombie movies and you think, 'Well, what if that zombie was, like, somebody that I love? Then that would be kind of (messed) up to shoot them in the head,"' she added, using an expletive instead of "messed."

Once Plaza was onboard, the project came together quickly and they blitzed through the shoot in just 22 days.

Plaza at first thought of doing a zombie movie marathon for a week to help develop her character.

"And then I thought, 'But you know, zombies aren't real, at least I don't think they are, so really all those movies are just someone else's interpretation of what that is,"' she said. "So I decided to not do that and do the opposite and not watch anything and just try to create it on my own, using the script and then using the dark demon energy that brews under the surface of my soul."

She had to portray her character through about five stages of zombie deterioration. They didn't shoot in sequence, so Plaza used some clever tricks to remember which stage her character was at in terms of her "zombiness."

"I'm like Meryl Streep, I have a craft," she said, tongue in cheek. "(Beth) had a limp and I didn't want to ever forget that, because I was trying to keep track of so many things, so I did put a very sharp rock in my shoe (to remember).

"Every day Dane would be like, 'Take the rock out, it doesn't do anything,' and I'm like, 'You don't understand my process. I need this rock."'

Constantly thinking about such physicality while also showing a wide range of emotion was a challenge but fun, said Plaza.

"It was fun for me to try to remember, like: 'OK, so at this point I'm, like, not fully zombie, but I kind of want to eat people but I kind of don't know it yet."'

"Life After Beth" opens in Toronto at The Royal on Friday, when it will also be available on video on demand.