Frontal aspect of the circumstellar shell from Fig. 17 (simulation B4 after 11 800 years ) showing only those parts with log (n²) > 1 (left panel), log (n²) > 2 (centre panel) and log (n²) > 3 (right panel). The qualitative structure does not change much, but the amount of “empty space” between filaments increases and the filaments themselves are fading. A further reduction in visibility would remove the filaments completely and leave only a handful of knots.