“In sickness and in health” is usually a promise of unwavering devotion, but for Lili Reinhart, sickness unexpectedly became her saving grace while filming alongside BTS. The actor recently found herself at the center of the K-pop supergroup’s latest musical era after landing a role in the music video for 'SWIM.'

What began with an unexpected direct message from BTS’ creative director eventually took Reinhart all the way to Lisbon for a four-day shoot. But stepping into a BTS music video came with one major challenge she never quite saw coming.

And as Reinhart later revealed, getting through the shoot required a little more than learning the moves.

Lili Reinhart’s nausea unexpectedly worked in her favor while filming BTS’ 'SWIM.' Appearing on The Tonight Show Starring Jimmy Fallon, the actress revealed that she was extremely sick throughout the four-day shoot after a rough flight to Lisbon.

While filming on a boat, Reinhart said she was heavily medicated for the nausea and was essentially half-asleep as she swayed along with the music. The experience also helped ease one of her biggest fears about joining the video: having to dance alongside BTS.

"So I'm, like, kind of unconscious in the music video when I am on the boat. So, when we watch it again, it's not method acting. I'm just really heavily medicated," she said.

Reinhart told Fallon that she initially worried she would have to turn down the opportunity because she could not dance like BTS. The group’s famously demanding choreography intimidated her, but 'SWIM' allowed for a more improvised, free-flowing style. And feeling nauseous just made her God's favorite child. Reinhart shared that she was reached out to after BTS’ creative director reached out to her via DM, having seen her work on Hal & Harper.

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While her BTS experience gave her butterflies in her stomach (not in the best way), her upcoming The Love Hypothesis is set to give that to the book's fans, quite literally. And while BookTok is dying of anticipation, Reinhart went from being the worst at science to playing a Stanford scientist in this one.

Lili Reinhart and Tom Bateman have BookTok fans in a chokehold since the trailer came out, and Reinhart a little more, owing to her rom-com homage with her press tour fits. So on Jimmy Fallon, the discussion about her upcoming film was bound to happen.

For Reinhart, playing a Stanford scientist in The Love Hypothesis is quite the academic plot twist. The actor admitted that science was her “worst subject in school ever,” making the role a particularly amusing departure from her real-life classroom experience.

"I joked to my family, I was like, I'm playing a Stanford scientist," she said.

Based on Ali Hazelwood’s bestselling novel, The Love Hypothesis stars Reinhart as Olive, who enters a fake-dating arrangement with Adam, played by Tom Bateman. The story was inspired by Hazelwood’s Reylo fan fiction and follows the pair as their pretend relationship gets increasingly complicated. 

If BTS tested her stomach, The Love Hypothesis is putting Reinhart’s science skills to the test.

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What do you think about Lili Reinhart's dance moves in BTS' 'SWIM' video? Let us know in the comments.