When the upcoming James Cameron movie Avatar: The Way of Water was filmed, the actors involved faced a unique challenge: a lot of the film would be shot underwater.
The sequel to Avatar, which became the highest grossing movie ever at the box office — making $US2.9 billion ($4.3 billion), will follow the story of a refugee family displaced by war.
Directed by James Cameron, Avatar: The Way of Water stars Sam Worthington, Zoe Saldana, Sigourney Weaver, Cliff Curtis and Kate Winslet.
It's set to be released December 15.
The cast had to act through performance capture — where the actors wear markers and several cameras shoot simultaneously in order to generate a 3D character and place them in the fictional setting of the movie.
They also had to act underwater.
The film's star, Australian actor Sam Worthington, told ABC News this meant having to use true emotion and true feelings.
He said one high-stakes scene of a father and son emotionally connecting had to be acted without words.
"Now for me the scene I realised we were 30 feet underwater and running out of oxygen. And that wigged me out a bit — my heart rate went through the roof and that means you're losing more oxygen," Worthington, who plays protagonist Jake Sully, said.
"And then the kid just kind of looked at us and we reconnected and finished this heartbreaking scene and I think these things are incredibly difficult to do even on dry land."
Worthington said the actors had the challenge of conveying emotional scenes through expressions and gestures.
"For some crazy reason we've decided to do them underwater, and the whole movie takes emotional scenes, puts them in an environment that is foreign," he said.
Actors had to undergo rigorous underwater training, including how to hold their breath underwater for minutes at a time and free dive.
Winslet held her breath for seven minutes underwater, breaking a record set by Tom Cruise in Mission Impossible: Rogue Nation.
"Jim is raising the bar on storytelling, because when you're underwater, you can't use words to do these heartbreaking scenes. You're having to use true emotion and true feelings and a tactile response to get this message across," Worthington said.
The first Avatar was celebrated for its boundary-pushing CGI and visual storytelling techniques.
With a number of sequels in the works, the series has become one of the most expensive series of films ever made.
There's little revealed so far about the plot of the soon-to-be-released sequel, but the film will focus on the Sully family ten years after the first film, as they face another war.
The original film, released in 2009, is set in the 22nd century where humans are colonising a habitable moon called Pandora in order to mine a valuable mineral.
The film tells the story of Sully, who eventually falls in love with a Na'vi woman, Neytiri, from the local indigenous tribe.
"[In the first film] Jake, he found an affinity with a culture and an affinity with a different planet. Within that he found himself. I think this to me, personally, Avatar: The Way of Water is about protecting all of that," said Worthington.
At the heart of the Avatar films are themes surrounding capitalism, climate change, the endless cycle of war, colonisation and displacement.
Worthington says Cameron often uses his movies to explore these themes in deliberate ways.
For instance, 1997's Titanic dealt with class while the Terminator series explores hostile technology in an apocalyptic future.
"So one of the central themes is can we afford the life that we were extracting from our environment?" New Zealand actor Cliff Curtis, who plays new character Tonowari, said.
"As human beings, you know, what does it take to get an ounce of gold? What's the impact of what we're doing to our environment so that we can maintain our quality of life?"
In the sequel, Sully now has children with Neytiri and is navigating fatherhood with a growing brood.
When war causes his family to become displaced, he seeks out the help of Tonowari, the leader of a reef clan.
"We live as a reef people in the ocean. So we have a whole new world to explore and discover. And we take in these refugees — the Sully's.
"They turn up looking for refuge and culturally we have to accept them whether we want to or not, and then we have to show them the way of the water how to like live amongst us, and Jake brings a lot of baggage with him," Curtis told ABC News.
The sequel is being released 13 years after the original film, delayed a number of times due to COVID-19 and other production setbacks.
Cameron has previously said he had to wait for film technology to develop to be able to film the motion capture sequences underwater.
"Is he going to remain the great warrior that he ended up being? Or was he just going to be a dad? And that's his kind of journey in this movie: which is more worth fighting for?" Worthington said of his character Sully.
"That's a struggle, because it's the Na'vi that he chose and the love that he chose, so it's like, you've got this reckless kind of crazy warrior, but now he has such a level of responsibility and it's how do you balance that out?"
For Curtis, the central focus on family and being parents makes the film universally relatable, especially when raising kids and making decisions as a family can sometimes be a process of trial and error.
"You're trying to figure it out as you go. And I think Jim has captured that really well," he said.
"It's like, we want love, we want the love of others, [it's] when we want to express love. We want to be connected in a meaningful way. But no one gave us the rule book of relationships.
"It doesn't matter whether you're on Pandora or you're in Sydney, Australia or wherever you are. We're all trying to figure it out."
Worthington said the family's experiences are all too familiar.
"Yes this family is displaced and is on the run from war, but their arguments are about common domestic issues that we can all relate to … but it just happens to be during an intergalactic war."
