  Using a MeerKAT observation of the galaxy cluster A3562 (a member of the
Shapley Supercluster), we have discovered a narrow, long and straight, very
faint radio filament, which branches out at a straight angle from the tail of a
radio galaxy located in projection near the core of the cluster. The radio
filament spans 200 kpc and aligns with a sloshing cold front seen in the
X-rays, staying inside the front in projection. The radio spectral index along
the filament appears uniform (within large uncertainties) at $\alpha\simeq
-1.5$. We propose that the radio galaxy is located outside the cold front, but
dips its tail under the front. The tangential wind that blows there may stretch
the radio plasma from the radio galaxy into a filamentary structure. Some
reacceleration is needed in this scenario to maintain the radio spectrum
uniform. Alternatively, the cosmic ray electrons from that spot in the tail can
spread along the cluster magnetic field lines, straightened by that same
tangential flow, via anomalously fast diffusion. Our radio filament can provide
constraints on this process. We also uncover a compact radio source at the
Brightest Cluster Galaxy (BCG) that is 2--3 orders of magnitude less luminous
than those in typical cluster central galaxies -- probably an example of a BCG
starved of accretion fuel by gas sloshing.
