"To make an analogy, gene sequencing is like having a big pile of automobile parts dumped on the floor, and the scientists have to put it all back together again. But there's one big problem: they don't know it's a car - it's just a pile of parts. So they have to take every single little part and try to figure out all the places it could fit. Here's one little screw. You've got to find all the hundreds of different threaded holes it might possibly fit into. That one step narrows down the possibilities for that particular screw to a few dozen, and takes an enormous amount of computing. "