If you ran your hand along a shark from nose to tail, the skin would feel surprisingly smooth. Go the other direction and it feels like 80-grit sandpaper rough enough to scrape off your fingerprints. The difference is millions of tiny tooth-shaped scales called dermal denticles, all pointing toward the tail.
Each denticle is genuinely a miniature tooth - same enamel, same bone-like base, same shape. Sharks are basically swimming around in armor made of teeth.
The shape isn’t just defensive. The denticles channel water smoothly across the shark’s body and break up turbulence as it swims, which both makes the shark faster and makes its motion almost silent. Swimsuit makers actually copied the shark-denticle pattern to design super-fast competition swimwear in the early 2000s - until the suits got banned for giving an unfair advantage.
