Yeah, when I saw this thread I was going to bring up Fast Food Nation as well.
It's amazing how many foods "natural flavor" is in. I highly doubt that it has anything to do with it being animal derived, as I've seen natural flavor in anything from Silk to crackers to pretty much any and all organic vegan packaged food.
Basically, when you eat "natural flavor" you are eating the same flavor chemicals as when you eat "artificial flavor" - only those chemicals are derived from a natural food source. For instance, artificial banana flavor is made from mixing chemicals together, and natural banana flavor is derived from a banana - but in the end you have two test tubes with two identical chemical compounds.
I've tried to avoid "natural flavor" since reading about that, but it's nearly impossible unless you avoid packaged food altogether.