He drew an oval shape to the left of the board, a doorway to the centre and a noose to the right. ‘Here-’ - he indicated the oval- ‘We have the population of London, gathered together in a single mass. Our door here will admit just one of these millions, so acting as a filter. This individual is the one suited for the noose, the man we shall see hang.’ ‘But, Holmes-how do we make the correct selection?, the odds must be several million to one.’ ‘Let us see if we can lower those odds. - Holmes to Watson, Sherlock Holmes and the Whitechapel Murders