
Revealing mistake: When Chocolate Mousse throws the anchor with the rope attached into the air, if you watch the ground when they run away, you can see that there's suddenly a lot more rope there, revealing that it was filmed in two takes and the anchor wasn't really thrown directly above their heads. (01:11:20)
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.