Grammy winner Finneas OConnell, aka Billie Eilish s big brother, spilled some fun secrets on The Tonight Show starring Jimmy Fallon Monday. (See the video above.)

OConnell said he and his superstar sister have taken to recording everyday sounds to expand what he called the tool box of material they use in their music collaborations.

Eilish, for instance, came home from an appointment for her Invisalign teeth straighteners with a recording of the high-pitched sound of a grinding device, recalled Finneas, who often goes by only his first name. The blood-curdling noise made it into the song Bury A Friend.

The woodpecker-like tapping of a pedestrian crosswalk warning in Australia became a rhythmic addition to the megahit Bad Guy.

Genius. The siblings combined last month to win 10 Grammys (some shared), so a peek into their creative process is a treat.

Hear the results and Finneas interview above.