Finally, we note that the consequences of the FeCZ might be strongest in Wolf-Rayet stars. These stars are so hot that the iron opacity peak, and therefore the FeCZ, can be directly at the stellar surface, or — to be more precise — at the sonic point of the wind flow \citep{hl96}. This may relate to the very strong clumping found observationally in Wolf-Rayet winds \citep{1999ApJ...514..909L,2006ApJ...639L..75M}, and may be required for an understanding of the very high mass-loss rates of Wolf-Rayet stars \citep{1995ApJ...448..858E,hl96}.