Our tiny dive boat bobs on the crystal blue Flores Sea, about a mile from the primitive Indonesian villages along the shore. I tighten my fins, swig a few test gulps of air through my scuba gear and am about to roll in. Suddenly, a black beast the size of a minivan explodes out of the water. The enormous splash rocks the boat. "Manta ray," our divemaster says. "They're showing off. Like puppies. Okay. Now you, jump in."

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