[On the theory that one or more of the 9/11 airliners had an underbelly missile "pod."]
I started to take this theory seiously when it became clear to me that they wouldv'e needed a sure fire way to ignite all that jet fuel - ( there was a myth-busters episode on Discovery once where they tried to blow up a tank of gas by shooting at it, and couldn't do it, not even with phosporous tipped tracer-bullets. They decided that the myth that you can blow up a fleeing car by shooting at the gas tank is bunk.)
A "pod" was probably overkill (you don't need a cruise missile to light a cigarette) , but I'm beginning to believe it. They wanted to make sure all that fuel got lit before it spilled all over the place and evaporated.