Cartoon illustrating how a relatively small tilt between the plane of the jet-loop structure and the disc of M 51 can result in net redshifted or blueshifted velocities on alternating sides of the galaxy (because M 51 is almost face-on). The differences between HCN and CO kinematics in Fig. 8, with hints of redshifted material in the east of the northern loop and blueshifted in the west, could be indicative of the situation suggested by the right panel of this cartoon.