You raise a good question. That object can be seen in other videos of the same event.
The debunkers will claim it's a bird Sure, it's a falcon diving at mach 2!
I'll see if I can find the other videos that show it.
Naturally, this anomaly was never addressed by the media (it doesn;t exist)
This could be a very important clue to what really happened on 9/11, I believe it to be at any rate.