How do insect pieces get into peanut butter?

As peanut butter consists of ground up products, it's most likely made up out of the 'ugly' peanuts unsuited for whole sale, so there might be a few bits and pieces of insect in there. You won't see them, though, as they've been ground up so well they can't be found (they're not actually whole legs). Same goes for other 'ugly product' foods such as Apple sauce and tomato soup.