Gary and I were in the water when we spotted a great brown patch of krill. Suddenly Gary hooted through his mouthpiece and pointed. Two whale sharks materialized out of the gloom, swimming rapidly about 20 feet apart. We were below them, so we couldn't see their open mouths, but we could see their bellies getting big as they went up, gulping mouthfuls of krill. Then they were gone, and so was most of the krill, as if two great reaping machines had passed through a field of grain.