Scientists 'discover' the secret of humour

Sigmund Freud thought humour stemmed from a feeling of superiority or incongruity, while Mark Twain suggested that its secret source was not joy but sorrow.
Now, scientists claim to have put an end to the argument once and for all. Humour, they say, stems from a benign violation of the way the world ought to be.
People find an incident humorous when it goes against the normally accepted way of things, providing it is harmless, the new research claims.