To fend off predators, the black-saddled pufferfish (Canthigaster valentini) famously inflates its body with water, much like a person puffing up his cheeks and holding his breath. But unlike the blue-faced human—and in contrast with scientists' expectations—the pufferfish does not actually stop breathing, researchers report online today in Biology Letters. Scientists placed the fish into clear plastic chambers where they could monitor their respiration. They then poked the puffers with a piece of tubing that sucked in water, simulating a predator attack. As expected, the fish responded by ballooning up and by rapidly gulping down water into a distensible stomach. And, contrary to previous belief, respirometers showed that the fish kept on breathing throughout the process. Scientists had suspected that during inflation, respiration might occur through the skin instead of across the gills, but this, too, seems to be false: Instead, the data and observations show that the pufferfish continued breathing with their gills as usual. In fact, compared with resting rates, the fish’s respiration increased close to fivefold during the inflation process. Even if they don’t stop breathing, the defense strategy is energetically taxing for the pufferfish; after the test, most took hours to return to resting respiration rates.