The gills allow the octopus to inhale oxygen and then exhale through a tube called a siphon. If an octopus breathes fast and exhales hard, it can swim backwards using jet propulsion. Oxygen is found in the atmosphere and in water. Aquatic creatures need to filter oxygen from the water and then discard the water so they don't drown.
An octopus breathes the same way all fish breathe, which is through the gills. The gills of the octopus are located inside the mantle cavity and exit to the outside of the body. Octopus oxygen needs are greater than those required by other molluscs and fish. Octopuses have three hearts, two of which pump blood through the two gills, where oxygen exchange occurs.
Octopuses breathe air (oxygen) through their gills. If an octopus comes out of the water, it won't be long before it dies of suffocation, since its gills aren't effective enough to breathe air. The beak-shaped mouth of an octopus is located in the mantle cavity at the back of the octopus's bulbous head, surrounded by the eight legs. It's not uncommon for octopus to come out of the sea.
Cephalopod experts say eight-legged nocturnal creatures are known to roam the shores at night in search of food. Octopuses near the coast often walk (actually crawl) overland in search of food among rocky puddles or if they are trapped at low tide. When the octopus swims, the heart of this organ stops beating, which explains why the species prefers to float rather than swim. Octopus gills are optimized to breathe only underwater and cannot be used effectively on land, for which the gills of some crabs have been successfully adapted.
Octopuses and other marine creatures need water to breathe through their gills just as people need air to breathe through their lungs. A woman in Washington once placed an octopus on her face to take a picture, and it bit her chin, causing severe bleeding. The lack of buoyancy that their gills experience out of water causes the gills to collapse on land, leading to a reduced surface area where little or no oxygen is absorbed and no carbon dioxide can be released (which acidifies the octopus's blood). This is the reason why the octopus can stay on land for brief periods of time and does not suffocate instantly like humans would underwater.
Blue-ringed octopus venom comprises the neurotoxin tetrodotoxin, which paralyzes the victim. To breathe, octopuses use gills for water exchange within the mantle cavity, which is the space between their arms. Breeding is a death sentence for male and female octopus, since both sexes die after breeding. For example, octopuses who had previously learned to attack a real ball can attack a virtual ball on a screen.
According to a study conducted by neurobiologist Robyn Crook at San Francisco State University, octopuses feel pain, both physically and emotionally, like mammals. The gills used by octopus are similar to those of squid, crabs, crayfish and lobsters, but somewhat less efficient.