  We have used an extension of our slow light technique to provide a method for
inducing small density defects in a Bose-Einstein condensate. These
sub-resolution, micron-sized defects evolve into large amplitude sound waves.
We present an experimental observation and theoretical investigation of the
resulting breakdown of superfluidity. We observe directly the decay of the
narrow density defects into solitons, the onset of the `snake' instability, and
the subsequent nucleation of vortices.
