Yuri or '...but sensei...it's been three years!'

There are often questions raised by beginner shakuhachi players with regard to technique and the production and use of yuri is no different.
To those unfamiliar with the term, it is the vibrato-like sound heard attached to shakuhachi notes when played. Non-Japanese unaccustomed to playing traditional wind instruments might suspect that this is accomplished by pulsing the diaphragm muscle similarly to some vocal vibrato techniques. In fact, that is one form of yuri found largely in modern music and known as ikiyuri, however this should not be confused with the more traditional type known as agoyuri where ago (pron. ahh-go)means chin.
There are typically three types of agoyuri:
1)tateyuri- produced by moving the head slightly up and down as if to nod 'yes'. This produces a distinct shift in pitch and is much easier to produce in the otsu and kan range than the dai-kan range.
2)yokoyuri- produced by moving the head from side to side as is to indicate 'no'. This produces a rising and lessening in intensity of sound with a slight pitch shift. Again, easier to produce in the lower two octaves than the highest. This is also the most typical yuri played when yuri isn't written into the score.
3)mawashiyuri- This is produced by moving the head in a repeated circular manner around the vertical plane. This less used type of yuri produces a dramatic effect of the two above types combined.
Attempts to play these techniques should be incorperated into your practice regime going from subtle to exaggerated and back to subtle. On both extremes, attempt to play yuri to the point that it breaks the sound. Develop the extremes.
There is a saying that all Japanese know: san nen kubi furi, which translates, three years neck waiving and refers to the ability to master the technique of yuri on the shakuhachi. I believe that one shouldn't accept that as a given. More properly it means that beyond the amount of time it takes to master getting a reasonable sound and being able to play all notes, flourishes like yuri can be attempted.
Good luck with it.