Billie Eilish gave fans a behind-the-scenes look at her acting debut in “Swarm” by posting photos of herself covered in blood on the show’s set.

The “Ocean Eyes” singer, 21, took to Instagram Sunday to share a slideshow showing her in hair and makeup for the Amazon Prime Video thriller.

In one selfie, fake blood dripped down Eilish’s neck as she flashed a menacing look while wearing a matted blond wig.

In another picture, she smiled despite her nose and cheeks being covered with fake cuts.

“eva,” the Grammy winner captioned the post, referring to the name of her character in the Donald Glover-co-created series.

She also included a photo of a sign outside her green room on set that read, “Do Not Enter.”

Eilish’s guest-starring role in “Swarm,” which premiered last Friday, marks the “Bad Guy” singer’s first acting gig — and her fans were not disappointed.

Several of her 108 million Instagram followers flocked to the comments section of her post to gush over her acting skills.

“Your acting was actually incredible! I feel so proud ????,” one fan commented.

“You are BRILLIANT,” a second agreed.

“IM SO PROUD OF YOUUUU,” a third exclaimed.

“you did so good in the show!” a fourth wrote.

“do horror movies next please im begging,” one more pleaded.

“Swarm” follows a superfan who is obsessed with a Beyoncé-esque pop star and embarks on a journey while committing murderous crimes along the way.

While the show is fictional, Eilish’s creepy role was inspired by the real-life NXIVM cult.

“There is a cult that existed in the world that was very prominent during that time,” Glover’s co-creator, Janine Nabers, told the Hollywood Reporter Sunday. “And that is the kind of true-crime element to that episode. And I think that when people think of the idea of artists or celebrities, there is this idea of thinking about the cult of Taylor Swift, or the cult of The Beatles or whatever.

“What we were really interested in was just seeing someone who worships at the altar of ‘something,’ and [exploring] this idea of what is the cult of the mind.”

Eilish expressed how grateful she was to be a part of the project.

“so much joy mannnnn @domfishback you are my idol,” she wrote on Instagram Saturday of the show’s lead, Dominique Fishback. “watching dom do her f–kin thing was one of the most amazing experiences of my life. this girl is f–king unbelievable.”

She added, “will cherish you forever dom love you so much.”

Eilish also said she felt “honored” to work with talents like Glover and Nabers.

“@donaldglover if it wasn’t for you i wouldn’t be the artist or person i am today,” she wrote. “@ibraake & @janinenabers you rock my socks off. truly can’t BELIEVE my reality sometimes. STREAM ‘SWARM’!! @swarmonprime ????????????.”

Other celebrities who make cameos in the series include Rory Culkin and Paris Jackson.