Saving Private Ryan - Gary Rydstrom (Commentary on DVD article)

Interesting infromation on this USC blog post

Of particular interest is:

The Omaha Beach scene contains moments in the water where the camera bobs above and under water. Rydstrom took the opportunity to create contrasting perspectives above and underwater. Above water the battle rages and Rydstrom describes it as ' chaos and cacophony.' Underwater the cacophony goes away and the water becomes safe, like a cocoon. By placing these two perspectives in contrast, Rydstrom is able to unsettle the viewer when bullets pierce into the cocoon and kill the soldiers. For the sound of bullets piercing underwater, Rydstrom demonstrates using an un-horrific sound for horrific effect. He used the sound of a fly-fishing line being ripped out of the water, which he had saved from A River Runs Through It.

Even when creating a "realistic" scene within a film, the sounds used are still taken from another source, entirely removed from the source given in the film.