In the episode "Fever", a white rat escapes from a laboratory where it is being used to incubate a possible cure for AIDS. The rat is found by the carouche Screed, who is on the prowl for dinner. When he feeds on it, the infected blood makes him ill; and he later passes the disease on to his friend Vachon.
As the corpse of the researcher is found at the lab, possibly a victim of foul play, Det. Nick Knight and his partner, Tracy Vetter, go there to investigate. Searching the area outside the building, Nick finds the corpse of the rat Screed killed. When he picks it up as evidence, he gets some of its blood on his skin, and it infects him as well. From him, the disease is passed to LaCroix.
Although a live animal was used for the laboratory scenes and the scene with Screed, a prop was made for the scene in which Nick discovers the bitten, bloody corpse. The actor who plays Screen, Greg Kramer, nicknamed the prop rat "Smokey". When he bit into it, it released a type of fake blood that has a strong mint flavor that he grew to hate.