I saw this in the news yesterday. While it wasn't in pet food, it should scare the bejabbers out of all of us, that this has gone on unchecked for a long time.
http://www.washingtonpost.com/wp-dyn/content/article/2007/05/30/AR2007053002227.html
It's disgraceful, nothing was actually done to stop this from happening in the future!