  Dark solitons in superfluid Bose gases decay through the snake instability
mechanism, unless they are strongly confined. Recent experiments in superfluid
Fermi gases have also interpreted soliton decay via this mechanism. However, we
show using both an effective field numerical simulation and a perturbative
analysis that there is a qualitative difference between soliton decay in the
BEC- and BCS-regimes. On the BEC-side of the interaction domain, the
characteristic snaking deformations are induced by fluctuations of the
amplitude of the order parameter, while on the BCS-side, fluctuations of the
phase destroy the soliton core through the formation of local Josephson
currents. The latter mechanism is qualitatively different from the snaking
instability and this difference should be experimentally detectable.
