I can whistle effing loud with my fingers. Useful when you have dogs. But I also do it at gigs to show my appreciation for the performers. If the person in front of me is holding a phone up, taking shite pics/videos of the gig I do it right in their pathetic little ear. B-)
I’d just figured out whistling with fingers at school when I saw a boy a year above doing the same without fingers. Stunned, I was! Spent flippin’ ages trying to recreate it. It’s easier if you start with low notes, and once you’ve got it, sliding from low to high at the right speed gets you a rather good impersonation of a whistling kettle.
No-hands whistling is bloody handy for alerting lemming pedestrians while urban riding.