With sharks, there is no theme music. Between Hollywood and The Discovery Channel, you can become familiar with sharks: their grace, their lethality, their cartilaginous skeletal systems. An actual encounter, as far as detail or knowledge goes, is largely superfluous. The sinuous way they move and the apparent lack of effort in currents that forces others to retreat, the frame of open ocean around the shark ? perhaps you don't get that without getting in the water.
The major impression one gets from a shark encounter is, in fact, that there is no background music, no Mantovani by way of John Williams, no escalating narrative. No overarching theme of death, or science, or stalking. There's just, suddenly, a shark ? more often, two ? invariably closer than one expects and moving in utter silence. Not that SCUBA diving itself is quiet; the bubbles from your regulator are surprisingly loud. But fish -- even large, deadly fish ? move in silence. This is, perhaps, the most unnerving aspect of a shark encounter. Not the confrontation with a dangerous animal, but the appearance, so close, with no announcement. It is a failure of our senses and this, more than the vanishingly small potential of a bite, causes us fear.
Once, in the Sea of Cortez, my wife and I were diving in the open ocean off a seamount. It was late Summer and the water was thick with plankton. We were deep, too, with no reference to the bottom and a plankton layer above us that made the surface invisible. It was as dark, I suppose, as evening.
Afterwards, we both described the same experience. The wall of hammerheads, hundreds strong, as far up, as far down, as far left and right as could be seen. We had both seen it for some seconds before it sorted out in our minds. And then in four or five breaths ? the metronome of diving ? each hammerhead in the wall changed direction, turned their tails to us, and moved effortlessly into the dark. We never saw the school again.
Another time, we were surfacing at the end of a dive ? again, a deep dive far from shore ? and again we had lost the bottom. This time it was a current and poor air management that had forced us to surface in blue water, with no references and far, far from the boat. We were shallow, perhaps fifteen feet below the surface, dawdling for the mandatory adjustment of partial pressures necessary to avoid "the bends." I don't remember why, I certainly don't remember any "sense of being watched" or rising hairs, but I suddenly twisted around very fast. A shark was swimming towards me, with deliberate intention.
Since, I've been menaced by sharks three times (the dive boat joke is to parse the difference between "threatened" and "menaced," with the punch line being that "menaced means: regardless of the facts, I was scared"). Each time, the eventual turning away, filled with grace and disinterest, was the most fearsome moment. The shark turns and swims away, no faster, no slower, no acknowledgement of the current that pulls you. At some point, the shark has been gone from sight for some breaths and your mind sorts it out and there's only again the frame of the blue ocean.