The singer just had a very special performance on the show, where she successfully tripped everyone out.
WATCH: How Billie Eilish walked on walls and performing on Saturday Night Live was SUCH an awesome illusion
Thankfully, Justin Theroux posted a BTS video of the studio and the snazzy equipment they used to make Billie look like she was walking on walls while performing on LIVE television.
Saturday Night Live
Billie wasn't really climbing the walls. Instead, the walls were moving. The whole 'room' was.
It was lifted and attached to a machine that rotated clockwise as Billie performed. She walked around normally, but it looked like she was walking upside down.
Saturday Night Live
The TV doesn't actually see the walls moving because the camera is carefully turning as the stage moves around.
IT'S GENIUS but would have taken a lot of practice. If Billie made one wrong move, it would have given the whole thing away.