Pressure slices during the instability growth phase of the fiducial Cygnus X-1 run CygX1. The color scale is fixed from 1 (blue) to 1000 Ba (red) to better highlight the beam structure. The beam shows alternating over- and underpressured zones whose number has risen at the 5000 s mark. The inner cocoon shows ripple-like structures alternating on either side of the beam with increasing intensity as the jet evolves.