"Aack." The muffled sound came as I felt Ellen's hand tightly grip my ankle. I turned quickly and caught a glimpse of the dorsal fin. It was five metres away, then four, then three when it made an abrupt turn and began circling us. The shark, about one and a half metres long, studied us with its cold beady eyes as it cut slowly through the reef. I turned with it, calmly facing the creature with my arms extended in front of me; intending to punch it in the snout with both fists if it came within striking distance. Ellen continued to grip my ankle. Then with an effortless sweep of its tailfin the shark suddenly vanished into the depths. 
 

We'd been snorkeling the outer edge of the reef off Drawaqa Island, Fiji. With pounding hearts we started for shore. After about ten metres I said to myself "dammit" and pointed back to the reef ledge. Ellen followed. If we'd swam off scared there was a good chance we might never go back out again...like the 'falling off the horse and getting right back on' theory. We snorkeled the reef ledge for a nervous ten more minutes. The shark didn't return.

 
Later, during a hand quivering cocktail, I started thinking about all the humans who could beat the crap out of me on my own turf, dry land. The shark was about my size, leaner, and likely about fifty times...hell maybe one hundred times faster than me underwater.
 

And I was going to punch it in the nose.
 

Realistically, the shark couldn't have eaten the whole thing. But it could have made a hell of a mess if it had taken a mind to.