Blink and you'll miss it. Shares bought and sold, profits made, no 'position' left and all in milliseconds.
High frequency trading is increasingly popular and said to account for a huge proportion of all share deals.
But could it bring the markets down? That is the fear of some people in the industry.
Paul Lewis interviewed Stuart Theakston, the head of high frequency trading at GLC hedge fund managers, and financial mathematician and critic, Paul Wilmott.
This item was first broadcast on Radio 4's Money Box on Saturday, 10 October 2009.