Hans Zimmer uses string sections as almost a "percussion" instrument in many of the themes for the Dark Knight trilogy, such as around the 2:00 mark here:

When a string section is playing a piece like this, is the bow moved back and forth rapidly for each of these notes, or is this effect achieved simply by rapidly changing the fret that is fingered on the keyboard while doing long, continuous bow strokes? (Boy, that last sentence sounds dirty...)

Just curious. I used to play the guitar, and feel like I should know this, but I'm not sure.