It just keeps swimming, just keeps swimming, swimming, swimming, swimming, swimming. Very likely the tightest opening sequence of all time, which you shouldn't mistake for most urgent. It knows when to pause, when to relish, when to make the first "Duh" longer than the second, bitey "Dun!" In trying to explain film form to anyone, my first question invariably is, "what do you think the opening of Jaws would be like if the John Williams score didn't come in while the camera was underwater, giving the audience a shark's eye view of the girl swimming? What would it be like if the motif doesn't switch as soon as the shark attacks - we hear her DUH DUN screaming, drawing frantic, DUH DUN breaths above water, but pitiless silence below?" Crap, probably, is the answer.