The Chihuahua, otherwise known as "Madness", is a small dog with a chipped ear, one brown iris and a stitch across its head. It has made several appearances over the course of the series. It has been dubbed "Madness" by the fans, seeing as Zim screamed "MADNESS!" upon seeing the dog in its first appearance in "Walk of Doom". The chihuahua might be a reference to a chihuahua mentioned in Johnny the Homicidal Maniac, when Nny screamed to a survey man that "This little chihuahua started following me".