  Recently, in an interesting work arXiv:1106.3972 a solution of the equations
of motion of massive gravity was discussed, and it was shown that one of the
fluctuations on that solution is superluminal. It was also stated that this
rules out massive gravity. Here we find that the solution itself is rather
unphysical. For this we show that there is another mode on the same background
which grows and overcomes the background in an arbitrarily short period of
time, that can be excited by a negligible cost in energy. This solution is
triggered by the parameter governing the superluminality. Furthermore, we also
show that the solution, if viewed as a perfect fluid, has no rest frame, or
that the Lorentz transformation that is needed to boost to the rest frame is
superluminal itself. The stress-tensor of this fluid has complex eigenvalues,
and could not be obtained from any physically sensible matter. Moreover, for
the same setup we find another background solution, fluctuations of which are
all stable and subluminal. Based on these results, we conclude that the
superluminality found in arXiv:1106.3972 is an artifact of using an
inappropriate background, nevertheless, this solution represents an instructive
example for understanding massive gravity. For instance, on this background the
Boulware-Deser ghost is absent, even though this may naively appear not to be
the case.
