[ Johan Liljencrants and John Page, UK, wrote recently about
 [ the motion of the reed as it oscillates.  -- Robbie

John Page has the more accurate description here.  High speed
photography shows that a properly curved tongue never actually strikes
the shallot.  The tongue flattens out with a very thin slit visible
between the shallot and tongue.

While it seems intuitively that the tip should finally hit the shallot,
some kind of whip action, the greater curve at the tip prevents this.
Flat spots or kinks will cause rattle, and another cause is a twisted
tongue, sometimes harder to diagnose because there are not flats or
kinks, yet the rattle is apparent.

John Nolte

 [ If a metal reed were electrically isolated from the metal shallot,
 [ a capacitance meter circuit would provide an electric signal which
 [ varies with the motion of the reed.  Modern conductive plastic
 [ material could be placed on the face of the shallot to yield a
 [ transducer whose conductance is in proportion to the contact area.
 [  -- Robbie