Lately I've noticed what look like long strings in my stool. They're white and motionless and far too long to be pin worms (they range from 1 inch to at least 8 inches). I do eat a lot of fiber (string beans, brocoli, tomatoes, raw vegetables, etc). Could that be it?
I've looked into parasites, but it doesn't seem to match up with anything specifically.
You may have caught "roundworms" from a dog... They live in your small intestine, and when they die, come out in your stool (so you wouldn't see them alive and rigglin').
Google some images of roundworms and see if this is what it looks like.
If it is, don't panic... Humans have lived with gutworms throughout their entire evolution. It's only recently that we've pretty much gotten rid of them. They are also fairly easy to fix.