This is a classic horror story set-up: a couple consumed by their own troubled chemistry moving into what film academics call 'the liminal zone’, a space between order and chaos, outside their normal life. The death of the kangaroo takes their crimes against each other into a wider world. They are now committing crimes against nature, for which they must be punished. Actually, the death of the 'roo is the second crime in the scene, after Peter’s starting a fire with his cigarette butt. His mention of the word 'recuperate’ is the first clue that Marcia has 'lost’ a baby. As the film progresses, it becomes clear that this is another crime, for which they are being punished, but it becomes less clear which was their 'original sin’ – her abortion, or his encouraging her to have the affair in the first place.