  It has been claimed that in stellar winds traversed by strong shocks the
mechanism for driving the wind by sound wave pressure cannot operate because
sound waves cannot propagate past the shocks. It is shown here that sound waves
can propagate through shocks in one direction and that this is a sufficient
condition for the sound wave pressure mechanism to work. A strong shock
amplifies a sound wave passing through it and can drag the sound wave away from
the star. It is immaterial for the sound wave pressure gradient that the sound
wave vector points towards the star. Since the strong shocks drag the sound
waves away, the star itself is the source for the sound waves propagating
towards it.
