Blake Lively learns to curse while filming A Simple Favor

When she was filming her new movie A Simple Favor, Blake Lively did not know what genre she had got herself into.

At our interview at the Crosby Street Hotel in New York City, she tried to explain.

"Each day, I was like, 'Is this a comedy or a thriller?' Because if this is just a straight drama, I am never going to work again because what I am doing is so over the top."

The 31-year-old US actress overcame her doubts and took the role because she desperately wanted to work with US director Paul Feig (Bridesmaids, The Heat, Spy and Ghostbusters).

"I said, 'I want in and I don't care what it is, and I don't care if he is asking me to do the catering, I want to be part of this movie,'" she said.

Described in its press materials as a stylish postmodern suburban noir, A Simple Favor - which opens here tomorrow - centres on Anna Kendrick's mummy vlogger who seeks to uncover the truth behind the disappearance of her best friend Emily (Lively), a glamorous but complicated woman.

British-Malaysian actor Henry Golding, who plays Lively's husband, was a complete unknown when he was cast in the film, Crazy Rich Asians not having opened yet.

Lively said: "I have heard people call him the new Cary Grant, which I think is a nice way to capture him because he has a bit of old Hollywood elegance.

"When we screen-tested with him, Paul wasn't looking for any specific type, he just wanted the best person for the role - someone who could believably be with both these women because our characters could not be more different.

"Every single one of the characters, what they are doing is terrible, but you still like them all."

She acknowledged that Golding was a bit nervous but "never really let on" about it.

"It is intimidating, being in a movie with this much dialogue and improvisation. But he came in every day just so cool and seasoned that you forget how new he is to it all.

"Paul creates a very, very safe environment, he makes you feel like you can't do anything wrong. And so I think that is really nice for Henry to be on a set like that, because they are not all like that."

The improv included a lot of swearing, which the habitually nice and polite Lively was not used to.

On how Feig made her come up with provocative things to say, she said: "Because each take would be improvised, we would be doing a different thing each time and he would be like, 'Instead of the s-word, let's try the t-word.' And I was like, 'The s-word, oh, okay.'

"When I am on camera, I can say the words from here to kingdom come, but as soon as they called 'cut', we were like speaking in code about the words because we were flustered to say them in real life."

FASHION

Like her character, Lively is a real-life glamazon who loves fashion and famously does not use a stylist. But what she is really addicted to is jewellery.

"It is an expensive addiction, but luckily one of my best friends is (US jewellery designer) Lorraine Schwartz. I get to borrow jewellery and give it back, but then there is always someone following me around reminding me it is not my own, like this bracelet," she said, gesturing to what she was wearing.

"I thought, 'Oh, this is so pretty, I could probably buy this.' It looks like nice crystals and pearls. And they were like, 'No, those are brown diamonds.' So I walk outside this hotel and I am terrified it is going to pop and there is going to be brown diamonds all over the streets in Soho and I am going to be on my hands and knees."

She joked: "My family was quite poor, so they didn't have much jewellery. But my mum, we can't wait for her to die so we can get all of her stuff. We are all fighting for that."

No interview with Lively would be complete without asking about her Canadian actor-husband Ryan Reynolds, with whom she has two daughters, aged four and two.

Will the couple - who met on the 2011 superhero flick Green Lantern - ever work together again?

"We have done our greatest work together - our family. That is the work I am the most proud of.

"But maybe one day. There is nobody I would love to work with more than him. But I would also have the hardest time working around him because I don't care what other people think, but I care what he thinks. So I would be really nervous... because I just want him to think I am awesome and not ever find out that I am not."

If you follow Lively and Reynolds on social media, you know they troll each other constantly.

"We poke fun at each other all the time. It is an organic thing. But yeah, all day long, we are just taking the piss out of each other, because he is my best friend. And I always win, and I am not competitive at all," she said with a laugh.

The writer is the president of the Hollywood Foreign Press Association, a non-profit organisation of entertainment journalists that also organises the annual Golden Globe Awards.