How to blow that loud whistle?

I learned it from my classmates in the third grade. I've been teaching for three days, blowing saliva every day to see if you can learn the method I said.

1:

Pinch the middle finger and thumb of the left hand (the middle finger and thumb are the largest and flattest, which is relatively easy, and can be blown at the back, and any finger can be used).

2:

Cover your teeth with your upper and lower lips (just like the old lady in the sketch)

The middle finger and thumb of the left hand are put in the mouth, which is more important. You see, the width of the first knuckle of two fingers is about the same as the width of the mouth. Just put it in your mouth, the side with nails is very flat, and your two fingers just turn into a triangle. see

4:

If you stick the tip of your tongue to your nails, it will sound like blowing a song with your mouth. Now looking at the size of the hole in the mirror, it is easy for the hole to make a sound without making a sound. The smaller the hole, the sharper the sound.

I don't know if you can use it, but don't worry. Remember, because you just learned to play, your hands will be full of saliva and even affect your voice. When there is no saliva in your mouth, just look in the mirror, as long as you reach the posture I said, compare step by step, wrap your lips around your teeth, and press the tip of your tongue against your fingernails. You can adjust the depth of your mouth by yourself, and you will certainly make a sound.