I can whistle with my lips just slightly open (like a ventriloquist).
I can make a really high pitched whistle like that and it confused the hell out of other people while they trying to find where the sound came from (high pitched sound is harder to pinpoint the location as it's bounce around the room).
But as I get older, I find it getting harder and harder to do so. 10 - 12 years ago I can whistle an entire song like that and it would sound crystal clear. Now it's really hard to follow a tune or make complex sounds.
Yeah that's what I meant. My lips can move freely while I whistle and it doesn't affect the sound at all. I just specifically mentioned the "slightly opened lips" as it's more interesting to the story I'm telling.