  Ram pressure stripping, i.e. the removal of a galaxy's gas disk due to its
motion through the intracluster medium of a galaxy cluster, appears to be a
common phenomenon. Not every galaxy, however, is completely stripped of its gas
disk. If the ram pressure is insufficiently strong, only the outer parts of the
gas disk are removed, and the inner gas disk is retained by the galaxy. One
example of such a case is the Virgo spiral NGC 4402. Observations of NGC 4402
(Crowl et al. 2005) reveal structures at the leading edge of the gas disk,
which resemble the characteristic finger-like structures produced by the
Rayleigh-Taylor (RT) instability. We argue, however, that the RT instability is
unlikely to be responsible for these structures. We demonstrate that the
conditions under which a galaxy's disk gas experiences ram pressure stripping
are identical to those that lead to RT instability. If the galaxy's gravity
prevents ram pressure stripping of the inner disk, it also prevents the RT
instability. In contrast, the stripped gas could still be subject to RT
instability, and we discuss consequences for the stripped gas.
