  Recent observations suggest that the long-duration gamma ray bursts (GRBs)
and their afterglows are produced by highly relativistic jets emitted in
supernova explosions. We propose that the result of the event is not just a
compact object plus the ejecta: within a day, a fraction of the parent star
falls back to produce a thick accretion disk. The subsequent accretion
generates jets and constitutes the GRB ``engine'', as in the observed ejection
of relativistic ``cannonballs'' of plasma by microquasars and active galactic
nuclei. The GRB is produced as the jetted cannonballs exit the supernova shell
reheated by the collision, re-emitting their own radiation and boosting the
light of the shell. They decelerate by sweeping up interstellar matter, which
is accelerated to cosmic-ray energies and emits synchrotron radiation: the
afterglow. We emphasize here a smoking-gun signature of this model of GRBs: the
superluminal motion of the afterglow, that can be searched for ---the sooner
the better--- in the particular case of GRB 980425.
