"the idea that sharks will drown if they stop swimming is a common one, but it's not entirely true. there are two main ways sharks go about breathing. ancient shark species breathed through a method called buccal pumping, which some of today's sharks still use. muscles around the sharks' mouths actively pull water in, sending it over their gill membranes and out the gill slits. the sharks absorb oxygen from the water as it passes by. lots of sharks that have adapted to bottom feeding use this method. some sharks' muscles aren't strong enough to actively pump water, though. called obligate ram ventilators — or obligate ram breathers — these sharks are the ones rumored to have to swim constantly to stay alive. in the past few decades, however, researchers have seen obligate ram breathers taking the occasional pit stop. for example, scientists have documented some species basking in underwater caves or on sandy seafloors, sometimes solo and sometimes in groups."