Octopuses are kind of like aliens. They are amazing in many ways. They have three hearts. They can walk, they can swim, and they can drive themselves forward at high speeds. They can change color and copy what other animals do and they even know how to open screw-top jars(带螺旋盖的罐子) and how to use tools!
Octopuses are mollusks(软体动物). But unlike many other mollusks, they don't have a shell. This allows them to pass through tiny spaces. Although octopuses mainly eat small fish, they are able to attack and kill small sharks.
One thing that makes octopuses seem like aliens is their blue blood. It is much better at giving oxygen(氧气) in cold and low-oxygen conditions than our red blood. Octopuses lose energy easily. This may help explain their outstanding intelligence: They can't run after their prey (猎物) for a long time. They must use clever tricks.
As a hunter (捕猎者), an octopus brings its prey under control through the use of a powerful poison (毒素). The smaller the octopus, the stronger the poison. The ten-centimeter-long blue-ringed octopus is so poisonous that it can easily kill a grown man. Octopuses themselves can be delicious prey to many different animals in the ocean, but many of the times they are clever enough to know how to keep themselves safe. With their color-changing skin, octopuses can easily "hide" themselves or flash alarming colors to frighten their enemies away. If that doesn't work, the octopus will send out a cloud of dark ink and quickly run away.
The most amazing part of an octopus is its arms. They can turn in any direction. The arms are too complex(复杂的) to be controlled from a central brain. Instead, they work almost independently. An octopus gives instructions and believes that they will be carried out. This means that the animal doesn't have a very good idea of where its arms are. They can't work out the shape of something by feeling it, like we can.
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