How to Hand Whistle (better method + detailed) 

1. Interlock your fingers rather tightly.
2. Cup your hands rather tightly.
3. Place your right thumb on your left index finger knuckle and your left thumb in the middle of your left index finger.
4. Blow into the space between your thumbs.
VIBRATO: Rapidly blow harder then normally repeatedly into your hands.
TIPS: Wash your hands to get the dust off, but then dry it to remove the water inside.
Don't blow spit into your hands.
Watch Mitsuhiro Mori's Childhood video (you can find it by searching "hand flute" in the youtube search box).
After hitting a note for the first time, separate your hands and do it again until it's consistent to build muscle memory.
Practice.
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