replaced them with someone else’s organs wi thout leaving any wounds or scars. An ex-
ample of a nonbizarre delusion is the belief that  one is under surveilla nce by the police, de-
spite a lack of convincing evidence. Delusion s that express a loss of control over mind or
body are generally considered to be bizarre; these include th e belief that one’s thoughts
have been “removed” by some outside force (thought withdrawal ), that alien thoughts have
been put into one’s mind ( thought insertion ), or that one’s body or actions are being acted on
or manipulated by so me outside force ( delusions of control ). The distinction between a de-
lusion and a strongly held idea is sometimes di fficult to make and depends in part on the
degree of conviction with which the belief is held despite clear or reasonable contradictory
evidence regarding its veracity. 
Hallucinations
Hallucinations  are perception-like experiences that occur without an external stimulus.
They are vivid and clear, with the full force and impact of normal perceptions, and not
under voluntary control. They may occur in any sensory modality, but auditory halluci-
nations are the most common in schizophrenia  and related disorders. Auditory hallucina-
tions are usually experienced as voices, whethe r familiar or unfamiliar, that are perceived
as distinct from the individual’s own though ts. The hallucinations must occur in the con-
text of a clear sensorium; those that occur while falling asleep ( hypnagogic ) or waking up