Is the recently discovered large scale filamentary feature Cattail in
  the cold or unstable phase?
  A recent publication (Li et al. 2021) discovered one of the largest
filamentary neutral hydrogen features dubbed Cattail from high resolution FAST
observations that might be a new galactic arm of our own Milky Way. However in
the analysis, it was suggested that this neutral hydrogen feature is cold
despite having 12km/s total linewidth. We evaluate the probability whether the
Cattail is actually cold neutral media via the newly developed Velocity
Decomposition Algorithm (Yuen et al. 2021a) and Force Balancing Model (Ho et
al. 2021a). We discovered that even with the inclusion of the galactic shear
term, the feature is still at the unstable neutral media regime. Moreover, we
also discover that the Cattail is two disjoint features in caustics space,
suggesting that the Cattail might have two different turbulent systems. We
check the spectra of the individual system separated via VDA to confirm this
argument. We do not exclude the existence of smaller scale cold media being
embedded within this structure.
