As mentioned in the main text, the reversal of the central jet in the nonlinear regime of the
wave generation using a cylindrical plunger is a robust effect observed in a broad range of the
plunger accelerations with cylinders of various lengths. The stability of the pattern can be
optimized by adjusting the excitation frequency, which affects the mode number of the cross
wave. The reversal of the jet direction appears to be independent of different driving
frequencies. Fig. S4 shows inward flow patterns produced by the cylindrical plunger (white
rectangle in the centres of the plots) at two frequencies, in the gravity and in the capillary
wave range.