Cave exploration often requires you to push yourself through narrow gaps in the rock. Cavers call such places squeezes. The tighter the squeeze, the greater the chance of damaging some vital life-support system. In these conditions a diver could easily become disorientated and that could be fatal. The flooded caverns can play tricks on you in other ways. What seems like air, isn't. It's just another kind of water. This is a halocline - a meeting of fresh and salt water. Fresh water from the jungle flows over the heavier salt water from the sea. The saltwater layer is extremely low in oxygen making it a particularly difficult place for animals to live. Yet some have managed it, like the remiped, one of the most ancient of all living crustaceans.


洞穴探险常常需要穿过狭窄的岩缝，探险者们把这些地方叫做“窄缝”。“岩缝”越窄，生命悠关的支援系统受损的可能性就越大。在这样的情况下，潜水员很容易迷失方向----而迷失方向就会有生命危险。水下洞穴还可能暗藏另外的危险。它看起来像空气，但它不是，而是另外一种水。这是盐度跃层，是淡水和海水相交之处。丛林中的淡水从更重的含盐海水上流过。盐水层中氧的含量极低，动物极难在其中生活，但还是有一些动物能做到，比如桡足动物，这是现存最古老的甲壳类动物之一。