Muk is the living manifestation of pollution and all things disgusting. Muk looks very similar to its previous form, Grimer. The main differences are that Muk is larger than Grimer, and has a wider mouth and smaller eyes. It is also usually depicted with its left arm being much larger than the right one. The toxicity of a Muk is also stronger than that of a Grimer. Just a drop of Muk's essence can turn a virgin lake into a stagnant, rancid swamp within minutes. The poison from a Muk has a negative effect on whoever touches it, ranging from a simple fever to death. Its footprints alone can cause influenza if a person or Pokémon were to come in contact with it. Muk likes warm and moist places, such as garbage dumps or sewers. They sometimes also reside in dirty back alleys and in cities where pollution is common. Despite its severe toxicity, Muk has the ability to control its toxins and will never deliberately cause harm unless provoked to do so.