Last week, in the middle of a concert, Sigrid suddenly started Cossack dancing.
"It came out of nowhere," laughs the singer, who's been called pop's hottest new prospect. "I just felt like doing it. I always like to scare people a bit."
The singer is not, it has to be said, a malevolent presence in the flesh.
Aged just 20, she's fresh-faced and fizzing with energy as she prepares for the first of three gigs at Brighton's Great Escape Festival.
Both her parents have flown in from Norway to watch. Her mum fusses that Sigrid hasn't washed her hair, even though she's about to be filmed by the BBC.
Something tells us Sigrid won't care: On stage she's unfettered, her arms flailing and face contorting as she performs her debut single, Don't Kill My Vibe.
She doesn't break out the Cossack moves, but it's a thrilling, freeing performance.
"I hate it when things are planned," she says. "The thing I love about being on stage is I can do whatever I want.
"There's one song in our set called Savage In Our Blood and it's a ballad, it's a sad song, but at some point I'm not singing, I just growl. And I love how people are going 'what the heck is going on?' I just love that.
"I love shifting between being super cute and aggressive. It's funny."
Don't Kill My Vibe is her calling card; a powerful declaration of independence written after a disastrous recording session with older musicians, who talked over her, patronised her and made "mean comments".
Sigrid bit her tongue, but the frustration poured out while writing with her friend Martin Sjolie.
"You shut me down, you like the control / You speak to me like I'm a child," she observes coolly, while building towards a killer chorus.
"You think you're so important to me, don't you?" she trills over a soaring synth line. "Well, I wanted you to know / You don't belong here".
While the lyrics were inspired by a bad day at work, they are malleable enough to apply to anyone who's ever been diminished or spoken down to. Perhaps that's why it's struck such a chord with fans, racking up 21 million plays on Spotify in the last two months.
Not by coincidence, it was also the song that earned her a deal with Island Records, who decided to sign Sigrid after just one listen.
"There are certain acts you decide you have to have and Sigrid was one of them," president Darcus Beese recently told MBW, describing how he sent a team to Bergen to tail the singer, ensuring no-one else got her signature.
She's followed up Don't Kill My Vibe with an EP that's crammed full of vibrant, forward-thinking pop.
Plot Twist is a deliciously catchy kiss-off to an ex-boyfriend, it's lyrics apparently composed by reciting Twitter memes ("shots fired!").
"I remember when I started writing lyrics, I was very grand," she explains. "I tried to use a lot of symbols, because I thought that's how songwriting should be - with imagery and metaphor.
"I figured after a while, maybe I should just write it as I would say in real life. So 'Do you need me to spell it out loud? You screwed it up. Plot Twist: Moved on and now you want me."
"That's the kind of thing my friends would say to me. This is how I talk."
The EP's final track, Dynamite, is entirely different. Not so much an acoustic ballad as tear-drenched companion piece to Adele's Someone Like You, it is a startlingly intimate song which was, incredibly, recorded in a single take.
In the video, the camera focuses unflinchingly on Sigrid's face, reflecting every fracture in her broken heart.
"It's a very honest song," she says. "It's almost awkward singing it, because it's so intimate.
"For me, the song is about having difficulties of having a private life when you're working so much," she says.
There's a pause. She reconsiders, then laughs. "I'm dating my microphone. That's the only romance I have time for."
Sigrid Solbakk Raabe was born and raised in the small town of Alesund, Norway, fringed by the sea and the mountains.
"I was a very shy kid growing up," she recalls. "I was definitely quirky. Me and my sister played a lot together. She's my best friend - and we would put on fashion shows.
"I started doing theatre when I was six years old. I played the king in 1,001 Nights and something just clicked in my head. I remember thinking, 'Ooh, I like being on stage' and I didn't look back."
After learning the piano, she would bash out cover versions by Keane, Coldplay and Adele in her bedroom, but changing the melody or the chords "just to make it more my own".
"That's when I discovered I like to make stuff, not just copy it."
But "I didn't think music was something for me," she says. "I wanted to be a teacher or a lawyer, so school was a higher priority."
In the end it was her brother, musician Tellef Raabe, who unlocked her potential.
"He was playing a show in our hometown and he wanted me to join him on stage," she recalls, "but he didn't want me to do an Adele cover. He said I had to write my own song.
"I guess he figured out I had something in me, and I just needed that little push."
Amidst the growing acclaim, Sigrid took a break from the public eye and went back to high school to finish her exams. She was all set to apply for a law degree when her parents intervened.
"They were really super-supportive," she says. "They were the ones who told me, 'I think you should try this. I think you'll regret your whole life if you don't try music.'"
Back in Brighton, mum and dad are in the front row at the Marwood Bar and Coffeehouse, cheering enthusiastically as the wooden floor sags under the weight of fans who've crammed in to see their daughter.
After this, she flies off to the US, where she'll make her TV debut on James Corden's chat show. She's also been chosen to appear in a high-profile campaign for a company she can only refer to as "the client" (it later transpires to be Apple Music).
In other words, Sigrid is on a one-way course to pop stardom, and she's taking it in her stride.
Within her team, the ever-expanding list of commitments has been dubbed the "2 Blessed 2 B Stressed Tour"; and the star is determined to keep her feet on the ground.
She's even got an song about it. Called Raw, it goes: "I could never fake it / No apologies for being me / I just want to be raw."
"This whole thing is very me. It's Sigrid," she declares. "I'm Sigrid on stage and I'm Sigrid now.
"I figured out it's just easier to be me all the time."