How to get my players to whistle?

Im a first time DM commiting the sin of running a homebrew campaign. I have included a lot of mythological creatures from various cultures and I want to include (what i think is) a skin walker from the Appalacia region in the U.S. Specifically because when you whistle at night the skin walker ( again not sure if that is the correct creature/cryptid) comes after that person.

What I want to know is how do i get them to whistle? Like those mentalist tricks or magic tricks etc. Its not a crucial part of the campaign but a super fun encounter i think. Obviously in the folklore the creature kills whatever whistles and the players in the case will be able to fight and kill the creature after a hard fight.

Can anyone help with how to do this? Thanks!

Tldr: want to know how to passively convince my player(s) to whistle for a fun encounter.