  The chiral vortical effect (CVE) was derived first for non-interacting
massless fermions. Recently, an alternative derivation of the CVE was suggested
which relates it to the radiation from the horizon of a rotating black hole. We
attempt to generalize the latter derivation to the case of photons and
encounter a crucial factor of two difference between the two ways of
visualizing the CVE. Reservations and possible explanations are briefly
discussed.
