Kate Hudson’s latest character is “actually quite sad.”

“She’s being held onto by this billionaire that she probably doesn’t like very much but feels tied to,” Hudson says. “She deeply needs to be validated and seen and heard to the point where it’s self-destructive. She always gets in her own way.”

No, Hudson is not in some new movie you haven’t heard about yet. She’s talking about Birdie Jay, the delightful comic confection she brings to life in “Glass Onion: A Knives Out Mystery.” Hudson says that when you analyze the flighty Birdie, her problems seem quite heavy but on screen, she flits through as comic relief.

“She’s an absolutely fabulous character with hilarious lines any comedic actor would love,” says Hudson, who rose to stardom with her Oscar-nominated turn in “Almost Famous” and became a rom-com staple with hits such as “Bride Wars,” “How to Lose a Guy in 10 Days” and “You, Me and Dupree.” 

While Birdie scans superficially as outrageous, Hudson says the script provided her with ability to ground her character in genuine emotions. “I don’t get to play complex comedic characters very often but here you could see what was motivating her desire to be the center of everything,” she says. “This was such a dream.” 

Hudson says all those layers were in Rian Johnson’s script from the get-go. “Birdie just popped on the page,” she recalls. “When I got to read it, I said, ‘Let me go bulldoze his door down.’ The highs and lows and nuances were all on the page. I just wanted to say, ‘Put me in, coach.’”

One reason she was so eager to go was she immediately felt like she could see and feel Birdie. “What leaped off the page was her movement and I think the dancer in me got excited,” she says. The first time I met Rian I said, ‘I know how she walks’ and I couldn’t wait to get into that. Her physicality was wonderful.”

Hudson also felt Birdie’s physicality was essential to understanding her character, even if audiences don’t consciously pick up on how it reflects her impatience and unhappiness. “She can’t sit still so her foot is going or she’s touching another person or touching her own clothes. She constantly has to distract herself with her movement.”

Those clothes she is touching are another memorable part of Birdie and Hudson says the clothing definitely informed the performance. “Costume is essential, especially with a character like Birdie, with her fluid and accessorized outfits,” says Hudson, who has at various points had her own fashion lines, including the successful athleisure brand Fabletics. “Jenny Egan did the costumes and she is very collaborative. The moment I got into the first fitting with her I could see Birdie Jay come to life. It was a bucket list type of wardrobe”

For all of Birdie’s “me, me, me” desires, Hudson also had to make sure she fit seamlessly into the cast (admittedly, almost all unhappy egomaniacs as well). She says because the film’s tone was so specific it was a challenge for the actors, but that the whole cast “encouraged each other to play more and have fun with that tone.”

That chemistry, she says, owes a great deal to Johnson casting as if he were throwing a dinner party. 

“I think he was looking at personalities as much as everything else,” she says, adding that off the set they’d frequently play their own murder mystery games at night. (“I was very impressed with Janelle’s commitment to everything,” she says of co-star Janelle Monáe. “They showed up for game night with a cape, mustache and top hat. Where on earth did they find a top hat and cape in Belgrade?”)

The on- and off-set bonding had the feel of a summer theater acting troupe. “It must look crazy from the outside with us being geeky about how much we love what we do,” she says, “but when you’re inside, it’s so meaningful and rewarding and nourishing.”