It is a phenomenon that is on the rise throughout the world: The number of cases of demonic possession - and demands for priests to carry out exorcisms - is, according to multiple sources, soaring.

Medical science remains sceptical. However, a Princeton-and-Yale-educated mainstream psychiatrist believes demonic possession is indeed very real - and claims that the majority of Americans agree with him.

With 25 years experience in a private psychiatric practice and as a professor at New York Medical College and Columbia University, Dr Richard Gallagher has a rare vantage point to observe human behavior. And then there is the inhuman.