Well, cargo is often transported via passenger jets. Personally, I don't think the point of this particular "bomb" was to blow up at all. I think it was sent out on a fact-finding mission to see if it could get through security. Apparently this is not the first time it's been done. I wonder if this is the "threat" that Europe has been waiting for the past month or so? At any rate, now the terrorists know a little more about how to use and abuse public transportation for their own ends.