They collect crustacean shells and other objects to build fortresses around their lairs.

They have venomous saliva. All octopus species are thought to have some venom that comes from bacteria living inside the animals. Most don't have enough poison to harm people. But a bite from a small blue-ringed octopus can paralyze a human adult in minutes.

They eat their arms when bored.

A captive octopus intent on escape flooded a California aquarium.

They have high-resolution vision, like humans do.

In most octopus species, it’s customary for the female to eat her partner after mating.

They can open childproof pill bottles.

A common octopus has about 240 suckers on each limb, and a particularly large sucker can hold up to 16 kg [35 lbs]. The suckers are also extremely sensitive; they can pick up subtle chemical signals and move individually, even folding in half in a pinching gesture.

Using a network of pigment cells and specialized muscles in its skin, the common octopus can almost instantaneously match the colors, patterns, and even textures of its surroundings. An octopus can change the color of its entire body in just three-tenths of a second. But the creature doesn't simply take on the general pattern of its surroundings. Instead, it often mimics specific undersea objects, like plants or rocks, to disappear into the underwater scenery.

Their ink contains a substance that dulls a predator's sense of smell.

They have short lives that typically last only a few years. Some species drop dead after just six months.

The standard English plural of octopus is octopuses. However, the word octopus comes from Greek, and the Greek plural form is octopodes. Modern usage of octopodes is so infrequent that many people mistakenly create the erroneous plural form octopi, formed according to rules for Latin plurals. However, all three inflections are technically correct nowadays.