Detail that gave Cate Blanchett 'low-level anxiety' on the set of her new film

Cate Blanchett has opened up about her "low-level anxiety" on set of her latest film.

The Aussie actress stars opposite Michael Fassbender in the new spy thriller Black Bag, but it wasn't the high stakes of the film that had Blanchett feeling concerned.

Instead, it was a particular tree built into the set.

READ MORE: Justin Bieber's honest statement as speculation mounts

Blanchett and Fassbender play a married couple, and inside their home is a glass-walled garden just off the dining room with a large tree completely enclosed in glass.

"It's very subtle in the background," Blanchett told People.

"So it seemed to me a metaphor about the way they all lived their lives is that there was so much life, but it was entrapped," she added of her and Fassbender's characters, both spies forced to keep secrets from one another.

"I had low-level anxiety for the health of the tree."

The set was built at Pinewood Studios in England and was the vision of production designer Phil Messina.

According to Fassbender, the whole thing felt very realistic.

"We had a full house to walk around in," he told People.

"You go up the stairs into the bedroom and our wardrobe-bathroom area – it was all built.

READ MORE: Nick Cave addresses 'obnoxious' comment from 25 years ago

"And various people on the crew were like, 'Oh, I want to take that oven and table and chairs.' It was so beautifully designed."

Black Bag sees Blanchett star as Kathryn St. Jean and Fassbender as George Woodhouse, two British spies married to one another.

As keeping secrets is the main part of their job, the two are often dishonest with each other.

Topics as small as the location of a business trip is often kept secret, placed into the so-called Black Bag.

"The weird thing about these characters is they work so closely with one another," Blanchett explained.

"And so they know operationally so much about one another and have a lot of information on one another, but yet they don't actually know what's going on with each other."

Black Bag is out in cinemas now.

FOLLOW US ON WHATSAPP HERE: Stay across all the latest in celebrity, lifestyle and opinion via our WhatsApp channel. No comments, no algorithm and nobody can see your private details.