Visible crew/equipment: When the "blind" spy is talking with the British agent, the lighting rigs are reflected in his shades a few times.
Continuity mistake: During the fight on the truck, we see Nick's jacket sleeves covering his arms completely, till the wrists. Then, the shirt cuff comes out of the jacket as they fight for the gun and then gets back inside by itself. (01:21:15)
Chosen answer: The actors were weighted down with lead plates. Oxygen tanks were kept just out of picture, and the actors used them to breathe between takes. The takes were short enough to allow the actors to hold their breath through them. The short takes were then cut together to appear as one long fight. Sound effects were added post-production.