Like other fish, sharks "breathe" through their gills, which are respiratory organs akin to our lungs. As water passes over the gill's membranes, tiny blood vessels extract oxygen from the water. Carbon dioxide waste also passes from the shark's blood and out of its body through the gill tissue. Other sharks use ram ventilation; that is, they ventilate their gills by swimming very fast with their mouths open. Some sharks, such as the tiger shark, can switch between buccal pumping and ram ventilation depending on quickly they're swimming. Some sharks, particularly those that are not active swimmers, such as nurse and bullhead sharks, breathe using buccal pumping. This method gets its name from the buccal (mouth) muscles that actively draw water into the mouth and over the gills, allowing the sharks to respire while remaining still