Ben Mendelsohn in Babyteeth and the bite marks of young love

Shannon Murphy’s Babyteeth begins with the most abrupt, unpromising boy-meets-girl encounter imaginable.

Ben Mendelsohn in Babyteeth

A teenage girl in a school uniform is standing on a railway station platform, a little apart from everyone else. The audio is heightened; we can hear her breathing in and out, above the noise of chatter from nearby schoolmates and public announcements over the loudspeaker. She looks down, breathes deeply — and in that instant someone slams into her from the right, knocking her sideways just as the train clatters into the station. Shannon Murphy’s Babyteeth begins with the most abrupt, unpromising boy-meets-girl encounter imaginable.

And that moment changes everything, Murphy says. Its significance is marked with a title — “When Milla Met Moses On Platform 4” — the first of many chapter headings that punctuate the movie. In an instant Milla (Eliza Scanlen) has been almost knocked off her feet by Moses (Toby Wallace), a loose-limbed young man in a baggy Hawaiian shirt, with a rat tail and face tattoos. She makes a sudden decision; rather than getting on the train with her classmates, she stays and hangs out with him.

The energy of that opening collision was important for all kinds of reasons, Murphy says. “The world of the physical is something I like to pay a lot of attention to.” When it comes to the younger characters in the film, this is significant, she says. “I think that age group is so connected to and disconnected from their bodies, in such interesting ways … they’re feeling things so ­intensely.” First as a theatre director, then as a filmmaker, Murphy has always focused on the language of the physical. “For me, if you could strip all the words out of a film or a play and just watch what people were doing with their bodies, I think you should still be able to understand what’s going on.”

She wanted Babyteeth to have an immersive, saturating quality, to use chapter titles to disrupt narrative expectations, to draw on a range of evocative, eclectic music “that fits purely into this world, that can be quite timeless … And I really wanted to make people feel like they were teenagers again”.

Babyteeth, Murphy’s feature debut, was selected for competition at Venice and, in the wake of it, she was asked to direct a couple of episodes of the third season of Killing Eve. Her film is based on the 2012 play of the same name by Rita Kalnejais, who also wrote the screenplay.

The story might seem familiar in outline, Murphy says. “It definitely sounds like a lot of things you’ve seen before, but the tone and the way that it’s handled is completely original. I was so struck by how funny and how moving it was at the same time. And of how I loved all those deeply flawed characters.”

Milla, we soon learn, is terminally ill. Her parents — Henry, a psychiatrist (Ben Mendelsohn), and Anna (Essie Davis), a pianist turned music teacher — are devastated and barely holding it together, as they contemplate the unthinkable. The arrival of Moses, disreputable and distracting, feels almost like the last straw. It’s not that their beloved daughter is in the hands of a dangerous or domineering character, however. Moses is a lost boy trying to figure out an angle, but doesn’t find it easy to understand what Milla expects or wants from him. It’s Milla who’s calling the shots, in a way, “She’s shape-shifting,” Murphy says. “She’s trying to redefine herself in the world, to push away from her parents and be the most authentic version of herself she can be.”

Murphy had the perfect cast, she says. “Two extraordinary talents, Ben Mendelsohn and Essie Davis, who are so experienced, mixed with Toby and Eliza, who are both building their careers but are still quite new.” What the four have in common, she says, “is that they are all risk-takers. They’ll always offer something different and be playful, and that’s the way I like to work”.

Wallace — who won Venice’s Marcello Mastroianni Award for best young performer — captures the unpredictable warmth of Moses, “a character the audience never expects to like”, says Murphy. As Milla, Scanlen has to create a figure who is constantly evolving, “in flux, accelerating her life so rapidly” as other characters revolve around her. “That was really challenging and Eliza just embraced it”, using everything from writing in character to creating an Instagram account for Milla that only Murphy could follow, not to mention learning to play the violin convincingly within a month.

Babyteeth might have a bleak subject matter, but it can find black comedy in desperation. Mendelsohn and Davis successfully exploit the absurd elements of their characters, as well as their raw vulnerability.

Henry, who shuts down all emotions, liberally medicates Anna in an attempt to keep hers in check, and develops a fixation with a new neighbour. Anna, brittle, sharp, conflicted, seems to allow herself to veer out of control. “She’s someone who is going to behave appallingly at times,” Murphy says. “And that’s why, for me, it was essential to cast Essie because Anna is a character who would be really easy to judge or criticise. But Essie understood her.”

Henry allows Mendelsohn to show a side of himself with which Australian audiences would already be familiar. “Ben is so well known to the rest of the world for doing very serious, dark-horse characters. But I think he was excited to come back to his comedic roots and play someone he really understood.

“Ben’s a father himself. And, he’s perfect for this kind of ensemble piece because he’s such a generous performer. So present for everyone, and also just a complete loose cannon. It’s like a tornado hits the set when he arrives. He has so much energy.

“He’s moving around dancing and singing non-stop. And then we call ‘action’, and he’s super-still and focused.”

Babyteeth opens in selected cinemas on July 23.