Illustration of the ejecta-unshocked CBM interaction in the ratter’s rest frame. The forward and reverse shocks travel towards the same direction in the unshocked CBM frame with four-velocity lower than that of the ejecta. The contact discontinuity, represented by the dashed line, is the surface on which the total pressures of the shocked CBM and shocked ejecta are equal. The arrows represent the four-velocity of the forward shock, shocked material, reverse shock, and ejecta.