NGC 4789 (sketch, top view) in a pure merger shock scenario. The geometry is reminiscent of the one in Ensslin et al. (1998, see their Fig. 2), although the origin of the sketched configuration is different. Here, NGC 4789 moves faster than the shock and eventually overtakes it. The ICM along the path of NGC 4789 can be enriched by relativistic particles. The shock crossing happened in the past. We can hope to identify some changes in radio properties (e.g., the width of the enriched region) somewhere downstream from the current position of the shock (red dashed line). The radio emission at the shock reflects a more recent history of the system. As demonstrated by the numerical simulations of Nolting et al. (2019), when the galaxy moves away from the shock, the material along bent jets moves towards the shock and can even cross it. This is depicted by the black wave curves.