Schematic view of two possible scenarios (shown at the same time) explaining the nature of the dark lane. The front view (left panel), as S106 is seen on the sky, does not allow us to distinguish between infall scenario (dark lane in green) or expansion scenario (dark lane in blue) of the gas in the dark lane. The middle view shows best the “accretion flow” scenario, i.e. how the (green) dark lane wraps around the equatorial waist of the hourglass-nebula. The right view shows how the (blue) dark lane, which is more detached from the nebula, is tilted towards the observer and dispersed. An animated version of this cartoon is available online.