Nicholas Lea was fitted with a mask with tubes for the scene where the alien black oil leaves his body. Lea said filming the scene was horrible, and the scene ended up having to be filmed again a few days later. The similar scene from the start of the episode with the submarine captain was accomplished with a dummy head. The depiction of the oil in this scene was originally filmed using a magnetic fluid pulled along with magnets, although the end result of this was deemed not be "menacing" enough, and looked "a little bit comic". To fix this, the sound stage used to represent the submarine's interior was rebuilt so it could be rocked back and forth, with the movement being used to guide the flow of a different liquid. This effect was then enhanced digitally in post-production. The black oil effect over people's eyes was accomplished by inserting the footage digitally in post production.