1. Octopuses have three hearts that pump blue, copper-based blood. 2. An octopus is a mollusk, like clams and shells; however, through <a href='https://www.factretriever.com/evolution-facts'>evolution</a>, it lost its shell. 3. Octopuses are found in all oceans at every depth. 4. All octopuses are venomous. Their venom contains enzymes that help digest their food. 5. Octopuses can remember and recognize individual humans. 6. All octopuses have short life spans. The longest living octopus only lives three to four years. Most of the smaller octopuses live for 6 months to a year. 7. The venom of a blue-ringed octopus can be fatal to humans. 8. Octopuses can change their appearance in less than 30 milliseconds. They change colors by expanding tiny pigment sacs in their skin called chromatophores. 9. The blood of octopuses (and other mollusks) is blue because of the oxygen-carrying pigment called hemocyanin. 10. Because the octopus's oxygen-carrying pigment (hemocyanin) isn't as efficient as hemoglobin, the octopus has evolved two accessory hearts. 11. The plural of octopus is not octopi because the word is Greek 'octopous,' not Latin. The Greek plural would be octopodes, but scientists refer to them as octopuses. 12. An octopus named Otto threw rocks and sprayed water on a light above his aquarium in order to short-circuit it. 13. Octopuses are oviparous, which means they lay eggs like chickens do. By comparison, humans are viviparous, which means they give birth to fully developed young. Some <a href='https://www.factretriever.com/snake-facts'>snakes</a>, including rattlesnakes, are ovoviviparous, which means the female lays eggs inside herself, the eggs hatch inside, and then she gives birth to live young. 14. In what is called 'autophagy,' bored octopuses will often eat their own arms. 15. Like <a href='https://www.factretriever.com/dolphin-facts'>dolphins</a>, <a href='https://www.factretriever.com/crow-facts'>crows</a>, and chimpanzees, octopuses are part of a special class of animals that can use tools. 16. Octopuses are believed to be the smartest invertebrate on the planet. 17. Octopuses have the largest brain of any other invertebrate. 18. Some octopuses can walk—and even run—on land. According to one veterinarian, chasing an octopus on land is like 'chasing a cat.' 19. Octopuses have been known to rip the stinging tentacles from a Portuguese Man-O-War and use them as weapons. 20. Octopuses are the only marine animal that can open a jar. 21. Nearly 2/3 of an octopus's neurons are in its arms, which means its arms can react to stimuli and function at a fairly high level even if they are separated from the body. 22. Octopus skin contains the same light-sensitive proteins as octopus eyes. This means its skin can 'see' and respond to light without information from the eyes or brain. 23. Octopus ink serves two purposes: it both hides the octopus, and it physically harms enemies. 24. An octopus's appendages are called arms, not tentacles. 25. If an octopus doesn't escape its own ink cloud, it could die. 26. The largest octopus in the world is the Pacific octopus, <span style='font-style: italic;'>Enteroctopus defleini. </span>It weighs up to 33 lbs (15kg) and has an arm span of up to 14 ft (4.3 m). It also has three hearts and nine brains. 27. The smallest octopus species is <i>Octopus wolfi</i>, which is about 1 inch (2.5 cm) and weighs less than 0.035 oz (1 g). 28. The mouth of an octopus is beneath its arms and has a sharp, hard beak. 29. There are no known freshwater octopus species. 30. An octopus can regrow its arms. They can regenerate without any loss of function, unlike when a lizard loses its tail. 31. Octopuses have a special arm for mating. During mating, the male octopus uses its 'hectocotylus' to insert sperm into the female. They have been observed holding this special limb close to the body while foraging, possibly to protect it. 32. The giant Pacific octopus can in swim in depths of up to 5,000 feet. 33. A tiny octopus that was discovered in the 1990s is so cute that researchers are considering naming it <span style='font-style: italic;'>Opistoteuthis adorabilis</span>. 34. Octopuses can not only change color, they can also change texture. 35. Octopuses do not have bones. This means that even large octopuses can fit through openings the size of a coin. 36. A baby octopus is about the size of a flea when it's born. 37. In a tradition known as 'The Legend of the Octopus,' fans throw octopuses onto the ice during Detroit Red Wings games. In 1995, someone even threw an octopus weighing 38 pounds. 38. After a male octopus mates, he becomes senile and soon dies.