Little Monsters director Abe Forsythe on Lupita Nyong'o, ukuleles

Australian director Abe Forsythe didn’t set out to make a horror movie. Or a zom-com. But that’s how Little Monsters, which screened at last month’s London Film Festival and arrives in UK cinemas this week, ended up. Most of the credit, he insists, is down to his little boy, who was the original inspiration for the movie.

The story of a school trip to a petting zoo which deviates from the itinerary when a hoard of marauding zombies shows up, the film is based “on his first year of being in school, in kindergarten, and it just ended up being a horror film,” Forsythe recalls. “I was on a school excursion with my son, his kindergarten teacher and 24 five year olds at the petting zoo that we used as a location in the film and we were driving along in a tractor train when the driver got out to investigate something up ahead. It was one of those ideas that just came to me. What if it was a zombie? How would you keep 25 kids from zombies? How would you stop their minds being corrupted as well?”

Yet the film remained very much a personal project, with Forsythe both writing and directing and the little boy Felix (Diesel La Torracca) echoing his own son. “My son has the same specific food allergies as Felix in the film. It was very scary for me to have to hand him over to somebody else to look after him and protect him. But he lucked out and I lucked out because his kindergarten teacher was amazing and not only did she look after him for his specific needs, but she opened up his eyes to the world outside for the first time – the world outside of me.”

That teacher is played by Oscar winner Lupita Nyong’o and her involvement was, in Forsythe’s own words, “a mixture of synchronicity and luck.” She was, for him, the number one choice for the role. “There’s an innate strength to the character but, at the same time, there’s a goofiness and a playfulness and a warmth. I know this now because of having the experience of working with Lupita, but she doesn’t have a single false note. She approaches everything with so much truth and I needed somebody to take that role as seriously as she took it. But I also needed somebody who could work with the kids and bring them through the story as well. We got the script to her and it just happened to coincide with her looking for something different and she was looking for a comedy. She didn’t want to do a zombie movie but she responded to the character and what the movie says and 24 hours after she read it I was talking to her on Skype. 24 hours after that she was on board.”

She got the comedy she was looking for – and something different as well, as the role involved her singing and playing the ukulele, neither of which she’d done before. And making sure she got to sing Taylor Swift’s Shake It Off was almost as big a challenge. “We struggled for six months before Lupita got involved,” says Forsythe. “We were told we could use it for a fee that was about 10% of our budget, but only if Taylor approved. I didn’t want to make this movie without the song because it worked so perfectly for the story. Lupita heard we were struggling and said she couldn’t make the movie without the song so she decided to write Taylor a letter and wasn’t going to let her turn us down. She sent Taylor an email and the very next day we had the rights.”

Forsythe’s background as an actor – he joins a long list of performers, such as Bradley Cooper, Greta Gerwig and John Krasinski, who’ve all moved behind the camera – gives him a built-in understanding of what an actor needs on set. He’s called time on acting, concentrating instead on writing and directing, but retains a great respect for actors. “There’s a short hand I use to help in directing them, by keeping out of their way, making them feel safe so that they can do anything and that they’re allowed to fail. It makes for a happy set. Every shoot is logistically difficult – just think what it’s like to make a horror movie with eleven five year old kids and some animals! – but the performance is the thing that makes the audience care and identify with the characters and have an emotional experience. That’s why I’m not interested in a lot of today’s movies – it’s all about the spectacle and not about the truth.”

He’s intrigued to see how the film’s Australian “in your face” humour plays out with British audiences. “It has a real basis in the humour from over here. All my upbringing was with British humour, especially from the TV – Monty Python, Rik Mayall, Adrian Edmondson, Blackadder – and for my parents it was The Goon Show on the radio. It’s so engrained in our DNA.” And, when it opens this Friday, he’ll find out …..