Sharks are the only animals that never get sick: they are immune to every known disease including cancer. Their body frames are not made up of bones – they are made of cartilage, the tough, fibrous tissue that shapes our noses and ears. Instead of scales shark skins have small tooth-like spikes that are so sharp that shark skin has long been used as sandpaper. It is thought that some types of big sharks, including the Great White, change sex when they reach a certain size: males become females to ensure survival of their species.
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