The power, the grace, the agility. And after you have spent just a little time in the water with them, you start to learn their nature and how to read them.
In many ways, I am way more comfortable in the water with sharks all about, than I am with unknown dogs. You see, a strange Rotweiler might (or might not) be very aggressive - or worse - unpredictable. The thing with most sharks is that they are generally rather predictable. Here is a video I made a few years ago off the coast of South Africa.
To be completely honest, even I had a "what the frig am I doing" moment when I first saw the tiger shark pull up next to the boat - there seems to be some deeply inbedded instinct that when you see a very big shark pull up next to the boat, that you SHOULD NOT get in to the water. We got in to the water anyway and - quite predictably - everything was just fine. In fact, it was a dream.
Although I love the predatory sharks, they have nothing on a whale shark! I really should post some photos and stories on whale sharks some time.