Evolution of the density and magnetic field after the horizontal perturbation. The figure shows the dipped part of the flux rope. Panel a demonstrates the motion of the prominence just after the perturbation; panels b, c: lagging of the bottom part from the rest of the prominence body, and panels d, e demonstrate the zigzag shape of the motions. Panel f: state of the prominence in the final stage of simulation. The dashed lines indicate the magnetic field lines before the perturbation. The yellow lines represent the density isocontours.