  We study the dynamics of knotted deformable closed chains sedimenting in a
viscous fluid. We show experimentally that trefoil and other torus knots often
attain a remarkably regular horizontal toroidal structure while sedimenting,
with a number of intertwined loops, oscillating periodically around each other.
We then recover this motion numerically and find out that it is accompanied by
a very slow rotation around the vertical symmetry axis. We analyze the
dependence of the characteristic time scales on the chain flexibility and
aspect ratio. It is observed in the experiments that this oscillating mode of
the dynamics can spontaneously form even when starting from a qualitatively
different initial configuration. In numerical simulations, the oscillating
modes are usually present as transients or final stages of the evolution,
depending on chain aspect ratio and flexibility, and the number of loops.
