Know what I was thinking about yesterday? I saw a mark on someone's fingernail, and I remembered that when I used to play marbles, I would get a mark like that on my thumbnail.
It came from the way I held the marble, (aggie in some parts of the country), prior to "shooting" it.
I never could get the high-speed launch that some could achieve, but I had pretty good accuracy.
Never could do that piercing whistle between the teeth, either ...
Neither could I, but I could do an ultrasonic whistle. People would hear a small noise not audible more than a couple meters, but dogs would respond at many times that distance.