 At the police station the officers talk about the metaphysical proof  of precognition. Chief Anderton (Tom Cruise (qv)) rolls a red ball  along a table to demonstrate the law of cause and effect to Det.  Witwer (Colin Farrell (I) (qv)). All of this is an allusion to the  philosopher David Humes famous claim that by observing billiard  balls you can actually demonstrate that cause and effect does not  exist but is merely a habitually created fiction of the mind.