  GRB 030329 is unique in many aspects. It has a very low redshift for a GRB,
$z=0.1685$, and is therefore very bright and easy to monitor, making it the
most well studied afterglow to date. It shows a supernova bump in the light
curve, with a spectrum very similar to SN 1998bw, thus establishing with much
better confidence the connection between GRBs and core collapse SNe. There are
also two important physical characteristics that make this burst especially
interesting, aside from its remarkably low redshift. First, unlike most GRB
afterglows, the light curve of GRB 030329 shows a very large variability a few
days after the burst. These fluctuations show a roughly constact amplitude, and
a constant duration $\Delta t$, while $\Delta t/t$ decreases with time $t$.
Second, its $\gamma$-ray energy output and X-ray luminosity at $10 $hr are a
factor of $\sim 20$ and $\sim 30$, respectively, below the average value around
which most GRBs are narrowly clustered. We consider several interpretations for
the variability in the light curve, in the context of different physical
mechanisms, and find that the most likely cause is refreshed shocks, i.e. slow
shells that are ejected from the source and catch up with the afterglow shock
at late times. In GRB 030329 this happens after the jet break, which implies an
approximately constant duration $\Delta t$ of the bumps, in agreement with the
observations. This interpretation also explains the anomalously low initial
energy of this burst, as the total energy of the afterglow shock is increased
by a factor of $\sim 10$ due to the refreshed shocks, thus bringing the total
energy output close to the average value for all GRBs.
