  There is evidence that the star formation process is linked to the intricate
net of filaments in molecular clouds, which may be also due to gas compression
from external triggers. We studied the southern region of the Perseus NGC 1333
molecular cloud, known to be heavily shaped by similar external triggers, to
shed light on the process that perturbed the filament where the Class 0 IRAS4
protostars lie. We use new IRAM-NOEMA observations of SiO and CH3OH, both known
to trace violent events as shocks, toward IRAS 4A as part of the Large Program
Seeds Of Life in Space (SOLIS). We detected three parallel elongated ($>$6000
au) structures, called fingers, with narrow line profiles (~1.5 $km s^{-1}$)
peaked at the cloud systemic velocity, tracing gas with high density (5-20
$10^5 cm^{-3}$) and high temperature (80-160 K). They are chemically different,
with the northern finger traced by both SiO and CH3OH ([CH3OH]/[SiO]~160-300),
while the other two only by SiO ([CH3OH]/[SiO]$<$ 40). Among various
possibilities, a train of three shocks, distanced by $>$5000 yr, would be
consistent with the observations if a substantial fraction of silicon, frozen
onto the grain mantles, is released by the shocks.We suggest that the shock
train is due to an expanding gas bubble, coming behind NGC 1333 from the
southwest and clashing against the filament, where IRAS 4A lies. Finally, we
propose a solution to the two-decades long debate on the nature and origin of
the widespread narrow SiO emission observed in the south part of NGC 1333,
namely that it is due to unresolved trains of shocks.
