Naru Ro or 'Honking' ~ overtones

Recently I have been investigating the meaning of a Honking Ro or honkin in general. A shakuhachi is not a car so I am not fond of the term honk and doesn't do it enough justice. The honking or Naru (see below) is more than that I believe. It is about changing the tonal characteristics of the note, it is about enhancing certain frequencies or natural overtones and speed op power of blowing is also relevant. Tone of this flute is characteristic and also one of its main features. There are little other instruments on which you can alter so much in the tone, the voice perhaps is most similar.
From the world discussion forum this soundclip comes which demonstrates the Honking very neatly:

This clip or soundbite was posted by Edosan and is by Aoki Reibo playing Sarashi.

I would also cite parts of Chikuzens comment on this matter:

Honking" in Japanese is called "naru" or, it's a verb, "to naru". There are varying degrees of this. Some types of names have been offered here, "honking" and "growling", etc. It would be useful to have a common vocabulary but it has to built out of shared experiences. It's a bit subjective too without the audio references. Big fat jinashi flutes don't usually "naru" according to jiari players but they glow, growl and snarl. However, jinashi people (people who play mostly jinashi) use the word "naru" also but it points to a different sound...

... There are always flutes out there that seem to "cross the lines" but in general, the jinashi flutes that "naru" usually have a narrow bore and jiari flutes that don't "naru" usually have a big fat bore.

Another viewpoint would be that "honking" is like revving up an engine to hear it run and see what it can take. It takes technique in the embouchure and breathing which means......it takes technique. Some flutes do it more, some less and some not well at all.

The reason to practice this is that it's smart to practice something you can't do since you'll have to change how you play. If you are willing to do this (change) you'll learn something from it and maybe even develop technique if you do it long enough. You can always back off this "honk" when playing according to the energy that's appropriate to the song you're playing.

So ultimately flexibility is key.