A pufferfish at rest looks like a regular fish. When a predator gets too close, it gulps in water and inflates its super-stretchy stomach until it puffs up into a spiky balloon four times its normal size. Suddenly it’s too big to swallow.
Most pufferfish do this with water, not air, which means they can puff up underwater where most threats actually happen. If they’re pulled out of the sea, some can switch to gulping air - but it’s risky for them, so they only do it as a last resort.
Inside their bodies they carry tetrodotoxin, one of the deadliest natural poisons known to science - far stronger than cyanide. It’s a defense against being eaten. In Japan, a kind of pufferfish called fugu is served in restaurants by specially trained chefs who must remove every poisonous organ. One mistake can be deadly.
