It's been three days since Billie Eilish turned Saturday Night Live upside down with her ambitious performance of "bad guy," during which she danced on the walls like it was no big deal at all. Now, SNL has released a behind-the-scenes vid that sheds light on how the gravity-defying stunt came together — and there's a surprising source of inspiration behind it.

In the new vid, Eilish explains that her performance was influenced by a scene from the 1951 movie Royal Wedding, in which Fred Astaire dances on the walls and ceilings. Eilish and the SNL team pulled off the same trick by essentially making a rotating replica of the stage and shrinking it into a box with a camera attached to it.

"It's pretty disorienting," Eilish said of the nifty set-up. "It's not scary, ever. It's been only fun. For me, it was pretty easy to understand and get the hang of. The fact that they even trusted us to pull this off is really big because I don't even know if I would've."

Check out the vid below to see how the performance came together — from Eilish conceptualizing the setup with a tissue box on her living room carpet, all the way up to the live debut. Oh, and did we mention that she did this whole thing with not one, but TWO sprained ankles?! The girl is truly in a league of her own.