There is only one problem.
I can do it and it is not silent. My father could do it, and I always remember when I was a boy, wondering how he could make it happen, when I couldn't do it myself.
When my hands got bigger I somehow realised that I could do it too, and I have gently made fun of my own children in the same way that my father did of me. At last one of them can do it too - albeit quietly. With practise he can carry the tradition to the next generation.
The recipe is to keep your fingers quite straight and close all four of them against your palm quite quickly. Perhaps it helps to have long fingers, and my family seems to have the genes for that.
Try it . . . and refute a Zen Buddhist!