Robert Holmes and Rodney Bennett disagreed over the ending. Bennett disliked the end of Holmes' story, which saw Noah draw the Wirrn out into the depths of space, away from the Ark. Bennett wanted the Wirrn to meet a more decisive end, and suggested they could be dissolved by water. Holmes rejected this notion, and instead amended episode four to have Noah blow up the shuttle with the Wirrn aboard.
There was originally a scene where Noah was to describe the dual ecstasy and torment of becoming a Wirrn, culminating with a plea to Vira to kill him, which she is unable to bring herself to do. This was cut for being too horrific.
This episode was watched by 10.2 million viewers on its original transmission.
This episode takes place on the Nerva Beacon in 16087.