Delusions are categorized as either bizarre or non-bizarre and as either mood-congruent or mood-incongruent. A bizarre delusion is a delusion that is very strange and completely implausible for the person's culture; an example of a bizarre delusion would be that aliens have removed the affected person's brain . A non-bizarre delusion is one whose content is definitely mistaken, but is at least possible; an example may be that the affected person mistakenly believes that he or she is under constant police surveillance. A mood-congruent delusion is any delusion whose content is consistent with either a depressive or manic state; for example, a depressed person may believe that the world is ending, or a person in a manic state (a state in which the person feels compelled to take on new projects, has a lot of energy, and needs little sleep) believes that he or she has special talents or abilities, or is a famous person. A mood-incongruent delusion is any delusion whose content is not consistent with either a depressed or manic state or is mood-neutral. An example is a depressed person who believes that thoughts are being inserted into his or her mind from some outside force, person, or group of people, and these thoughts are not recognized as the person's own thoughts (called "thought insertion").