Why do pufferfish inflate themselves?

When threatened, pufferfish can rapidly gulp water, and sometimes air, into a stretchy stomach and body cavity. This makes them swell into a much larger, spiny shape that is difficult for predators to swallow. Many species also contain tetrodotoxin, a potent neurotoxin that adds another layer of defense. The toxin is famous for making some pufferfish, including fugu, highly dangerous if improperly prepared. Inflation is therefore only one part of a broader anti-predator strategy.