Sharks are fish. There are over 300 different kinds of sharks. White tipped shark. Wobbegong shark. Port Jackson shark. Grey nurse. Leopard shark. Some can be dangerous to humans, but most are not. The slits on the side of a shark's head are its gill slits. They need them to breathe. Most fish have scales. It's hard to see shark scales as they look like very tiny teeth. So their skin feels rough — a bit like sandpaper. (In the olden days they used shark skin as sandpaper! It was called shagreen.) The holes just above the mouth are nostrils Sharks can smell very well. They also have excellent hearing and can feel small vibrations in the water. They can even find animals buried in the sand. Sharks have several rows of teeth. When the front teeth wear out they are replaced by new ones. Different sorts of sharks have different kinds of teeth. This is a grey nurse shark. It looks fierce and it can be, but it's not interested in humans unless we annoy it. It's teeth are used to grab fish or squid. The food is then swallowed whole. This Port Jackson shark has tiny teeth to grab and crush crabs and sea snails. Male sharks have claspers. They are 2 lumps underneath it's body. Female sharks don't have claspers. Some sharks lay eggs, others have live babies. Grey nurse sharks have live babies. Shark babies are called pups. Grey nurse sharks usually have only one or two pups. When they are born they are quite big. They can immediately see, hear, smell and swim just like mum. Mum doesn't look after her pups. They are on their own and have to find fish to eat. If they are lucky grey nurse sharks can live for about 20 years.