Chris Carter claimed to have been inspired to write the episode after his dog had worms, a situation he called "very disgusting". He also had been reading about the Chernobyl disaster and the extinction of species at the time and blended all three of these concepts when writing the episode. Carter described his mood while writing the episode, "I was in a funk when I wrote that episode. We were coming back from hiatus and I was trying to find something more interesting than just the Flukeman. I was irritated at the time and I brought my irritation to Mulder's attitude. Basically, he had become fed up with the FBI. They had given him what he felt was a low assignment, which was sending him into the city after a dead body. But lo and behold, he finds that this is a case that for all intents and purposes is an X-File. It's been given to him by a man he's never looked at as an ally, Skinner. So it's an interesting establishing of a relationship between them." Producer J.P. Finn described the episode as a departure from Carter's usual work as it did not deal with an alien subject matter.