They are intelligent enough to distinguish brightness, navigate mazes, recognize individual people, learn how to unscrew a jar or raid lobster traps.

[11] Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects.

[15] This can be understood through Henry's law, which states that the concentration of a gas in a substance is proportional to pressure and solubility, which is influenced by temperature.

[15] In doing so, it uses a jet mechanism that involves creating a much higher pressure in its mantle cavity that allows it to propel itself through the water.

[20] Ultimately, this creates circulation issues and is not a sustainable form of transportation, as the octopus cannot attain an oxygen intake that can balance the metabolic demands of maximum exertion.

[18] This number is affected by the activity of the animal – the oxygen uptake increases when the octopus is exercising due to its entire body being constantly exposed to water, but the total amount of oxygen absorption through skin is actually decreased to 33% as a result of the metabolic cost of swimming.

The tissues and muscles of the octopus use oxygen and release carbon dioxide when breaking down glucose in the Krebs cycle.

The capillaries that line the folds of the gill epithelium have a very thin tissue barrier (10 μm), which allows for fast, easy diffusion of the oxygen into the blood.

[22] The gills are in direct contact with water – carrying more oxygen than the blood – that has been brought into the mantle cavity of the octopus.

Gill capillaries are quite small and abundant, which creates an increased surface area that water can come into contact with, thus resulting in enhanced diffusion of oxygen into the blood.

[27] The octopus also has large blood sinuses around its gut and behind its eyes that function as reserves in times of physiologic stress.

[29] Its only compensation for exertion is through an increase in stroke volume of up to three times by the systemic heart,[29] which means it suffers an oxygen debt with almost any rapid movement.

[31] The blood of the octopus is composed of copper-rich hemocyanin, which is less efficient than the iron-rich hemoglobin of vertebrates, thus does not increase oxygen affinity to the same degree.

[33] The Bohr effect explains that carbon dioxide concentrations affect the blood pH and the release or intake of oxygen.

The newly oxygenated blood drains from the gill capillaries into the systemic heart, where it is then pumped back throughout the body.

Shadwick and Nilsson[30] concluded that the octopus circulatory system is "fundamentally unsuitable for high physiologic performance".

Since the binding agent is found within the plasma and not the blood cells, a limit exists to the oxygen uptake that the octopus can experience.

[31] Poiseuille's law explains the rate of flow of the bulk fluid throughout the entire circulatory system through the differences of blood pressure and vascular resistance.

The hemolymph, pericardial fluid and urine of cephalopods, including the common octopus, are all isosmotic with each other, as well as with the surrounding sea water.

[36] Octopuses have an average minimum salinity requirement of 27 g/L (0.00098 lb/cu in), and that any disturbance introducing significant amounts of fresh water into their environment can prove fatal.

[36] Sulfate and potassium exist in a hypoionic state, as well, with the exception of the excretory systems of cephalopods, where the urine is hyperionic.

[36] These long, ciliated ducts filter the blood into a pair of kidney sacs, while actively reabsorbing glucose and amino acids into the bloodstream.

[36] Temperature and body size directly affect the oxygen consumption of O. vulgaris, which alters the rate of metabolism.

The pericardial fluid has concentrations of sodium, potassium, chlorine and calcium similar to that of the salt water supporting the idea that O. vulgaris does not osmoregulate, but conforms.

The middle cytoplasmic region is the most active of the three due to the concentration of multiple organelles within, such as mitochondria and smooth and rough endoplasmic reticulum, among others.

The shape varies widely and are occasionally more electron-dense than the epithelial cells, seen as a "diffused kidney" regulating ion concentrations.

As an oceanic organism, O. vulgaris experiences a temperature variance due to many factors, such as season, geographical location, and depth.

Like all animals, they produce heat as a result of ordinary metabolic processes such as digestion of food,[39] but take no special means to keep their body temperature within a certain range.

[43] The low metabolic rate allows for rapid growth, thus these cephalopods mate as the water becomes closest to the preferential zone.

[19] The decrease in ammonia being excreted is also related to the metabolism of the octopus due to its need to spend more energy as the temperature increases.