Seeing sharks while snorkeling - a rare occurence - is exciting rather than scary. Usually they cruise by, obviously heading NOT toward us; I think they would just as soon stay away from people. The one exception is that we are wary of sharks while we are actively spearfishing. On this day Britt told me he saw a 4-5 foot reef shark, but I never caught a glimpse of it. A little later I had just speared a fish and was swimming on the surface back to the dinghy with it, and Britt called out, "Oh, there's the shark! It's right under you!" Needless to say my heart rate hit about 200, and I looked down, panicked - only to see it close to the bottom (30 feet down) and swimming off away from us. Phew! This is why when we spear a fish we immediately hold it up out of the water - sharks and other predators sense not just the blood, but also the erratic motion of an injured fish. In fact, later that day I speared a big bar jack at a nearby reef, and the darn fish swam away with my spear...and while I was chasing it, a grouper came out looking for a free meal and nearly ate MY fish before I was able to grab the spear and swim to the dinghy with it...but that's another story.