What a funny thing. Did you ever try it without the string?
I remember hearing you could make a long straight chalk line, but we never tried that to my recollection.
I think you needed something for them to focus on.
You could “feel” them relax after a minute or so - and that is when you knew you could gently release your grip.
We would back off quietly, trying not to giggle or otherwise alert them.
It was something that a kid down the street would bring a cousin or friend over to watch, it was so odd.
It was so consistently done, except on occasion a hen would not “relax”.
You would never be able to hold a rooster like that.
Especially a banty rooster. They are far too aggressive.
They would shred your arms if you tried to grip them. :)
They chase off, dogs, cars, people, etc. even at feeding time.