  We give an review the HBT puzzle, and argue that its resolution requires the
introduction of new physics close to the phase transition scale. We argue that
a candidate for this new physics is bulk viscosity, recently postulated to
peak, and even diverge, close to the phase transition temperature. We show that
such a viscosity peak can force the system created in heavy ion collisions to
become unstable, and filament into fragments whose size is weakly dependent on
the global size of the system, thereby triggering freeze-out.
