Even their scales are modified to allow them to slip through the water in ghost-like silence. But there are persistent reports from New Zealand of a type of shark that actually barks like a large dog. But no one knows for sure how, exactly, these sharks manage to bark. Like its close relatives, the Draughtsboard Shark can inflate itself like a pufferfish when threatened by a potential predator. If attacked underwater, any of these sharks can rapidly pump water into the forward portion of its stomach, increasing the fish's diameter up to three times.
Water is prevented from exiting the stomach by a ring of muscle called the cardiac sphincter.
The sudden increase in size is enough to startle or intimidate most would-be predators. After the danger has passed, the inflated shark relaxes its cardiac sphincter, allowing the gulped water to gush from the stomach and out the mouth. But, if caught by net or hook and line and rapidly hauled to the surface, a Draughtsboard Shark may sometimes inflate with air instead of water. The cardiac sphincter renders the Draughtsboard Shark's stomach reasonably air-tight. When the sphincter relaxes, trapped air passes out the shark's stomach in an explosive rush, creating a hoarse 'bark' as it goes.