I'm of the opinion that it's possible that both a small plane AND a missile hit the building, not just one or the other. Think of the planes that hit the twin towers, and the flashes that occured before they hit. A missile or some sort of incendiary device/weapon was launched/detonated beforehand--before the plane hit.
I think it's entirely possible that the same tactic was used here. Missile hits building, small plane hits shortly after. The "missile" could have opened a hole into the building so that the "plane" or whatever could enter without leaving much wreckage on the outside. This would explain why the video shows no plane (perhaps it came after those five frames?) and would also explain the cordite smell.
It would also explain any objects hit along the path. In my mind, a missile would have a hard time maneuvering on its own to hit the Pentagon at the angle it hit. It would have to be guided somehow, and specifically, it would have to be carried by something to achieve the reported trajectory.
This also validates eye-witness reports that a plane--not a lone missile--hit the building.
While it's still doubtful that a 757 could have possibly crashed into the building, a smaller plane with a "pod" attached, or perhaps some sort of military plane still could have. The ideas that a small plane or a missile hit are not mutually exclusive. I think they're simultaneously possible, and judging by what we've seen of the other attacks, probable. Let me know what you think.