  The result of Thouless, Ao and Niu (TAN), that the mutual friction parameter
$d_\perp =0$, contradicts to the experiments made in rotating 3He-B by
Manchester group. The Manchester group observed that $d_\perp <0$ at low
temperature and approaches 1 at high temperature. The reason of the
contradiction is that TAN did not take into account the Iordanskii force on the
vortex and the spectral flow force, which comes from the anomaly related to the
low-energy bound states of fermions in cores of quantized vortices. The
Iordanskii force is responsible for the negative $d_\perp <0$ at low
temperature, while due to the spectral flow $d_\perp$ approaches 1 at high
temperature. Relation of the spectral flow anomaly with the paradoxes of the
linear and angular momenta in gapless superfluids is discussed.
