Cyanide is a chemical that, when present in a Creature's body, causes the heart to stop beating, and it may be fatal if a cure is not administered in time. It is found in Creatures 2, Creatures 3, and Docking Station.
Cyanide can be found mainly in toxic plants: for example, the Sourgum Berry in C2. It is cured by feeding creatures Ashgum Berries (conveniently, they live right next to the poisonous Sourgums) or Cantharis Berries in C2, or by injecting sodium thiosulphite (C2) or sodium thiosulphate (C3/DS). However, the Ettins and Grendels that come with C2 cannot process sodium thiosulphite and thus cannot be cured.
There are no known natural sources of cyanide in Creatures 3 or Docking Station; however, the Bitter Almonds agent contains cyanide.