Fallback and dynamical evolution in two exemplary explosion simulations for an 11.0 ﹩{M}_{\odot }﹩ progenitor (left) and a 20.4 ﹩{M}_{\odot }﹩ case (right). The upper panels display the total fallback mass as function of time. The red line gives the incorrect result from applying the rhs of Equation (1) at all times. The “reflection time”, t_r, is at about the instant of the late, local maximum of the red curve. The previous, incorrect estimate of the fallback mass (Equation (1)) corresponds to a value close to this maximum. The rising blue line shows the correct evaluation according to Equation (2), the black line with the decaying trend the corresponding mass-accretion rate, ﹩{\dot{M}}_{\mathrm{ib}}﹩. The temporary increase of ﹩{\dot{M}}_{\mathrm{ib}}﹩ in the 11.0 ﹩{M}_{\odot }﹩ model at ∼2000 s is connected to the inward acceleration of matter by the first reverse shock that is created when the supernova shock passes the carbon-helium interface. The sets of lower panels display velocity (v; solid lines) and adiabatic sound speed (c_s; dash–dotted lines), pressure, density, and temperature profiles (from top to bottom) for selected instants around the “reflection time”.