In the beginning of the film, there is a long scene in which Bourne is running from the Marines in the US Embassy building. He finally finds himself on a fire escape with its ladder removed. First you must notice that neither of its railings are attached to the building, in any way. Jason starts to climb onto the roof of the building, as he does it is pretty obvious that he is being suspended on wires. If you watch closely you can even see the harness he is wearing under his sweater. It's very easily seen if you slow it down.

As he attempts to do this, the railing (which wasn't attached the building to begin with) becomes attached, but only long enough to break out of the building! Jason begins to fall...well his stunt double does anyway. You will see the double's much longer, curlier hair. Bourne clings to the roof for safety and then jumps back onto the fire escape which once again has no way of being attached to the building.