"What were they trying to keep out?"
The Mongols, that's what. There, I just spoiled one of the movies. :P
Seriously though, the funniest thing about the Bourne series is that he always demands that his female sidekicks change their appearance as much as possible...yet he never once attempts to do the same.
Those 2 explosions...is the same explosion copy/pasted and slightly resized...
This was just great. The flat bit made me grin like a fool.