Christopher H. Bidmead had conceived of the Tractators as being able to curl up into a ball, killing their victims by encircling and smothering them. With this in mind, Ron Jones hired dancers and actors with similar skill sets to play the monsters. Unfortunately, visual effects designer Dave Havard's realisation of the Tractators was very constraining and inflexible, forcing Jones to abandon these plans.
This episode was watched by 5.8 million viewers on its original transmission.