  Recently, it was proposed that phonons are specularly reflected below about
0.5 K in ordinary single-crystal samples of high-T_c cuprates, and that the
low-temperature thermal conductivity should be analyzed by fitting the data up
to 0.5 K using an arbitrary power law. Such an analysis yields a result
different from that obtained from the conventional analysis, in which the
fitting is usually restricted to a region below 0.15 K. Here we show that the
proposed new analysis is most likely flawed, because the specular phonon
reflection means that the phonon mean free path \ell gets LONGER than the mean
sample width, while the estimated \ell is actually much SHORTER than the mean
sample width above 0.15 K.
