The majority of octopuses have almost entirely soft bodies with no internal skeleton. A beak, similar in shape to a parrot’s beak, is their only hard part. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from morays or other predatory fish.
Octopuses often break out of their aquariums and sometimes into others in search of food. They have even boarded fishing boats and opened holds to eat crabs.
In laboratory experiments, octopuses can be readily trained to distinguish between different shapes and patterns. They have been reported to practice observational learning, and have also been observed in what some have described as play: repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them.
Because of their intelligence, in some countries octopuses are on the list of experimental animals on which surgery may not be performed without anesthesia. In the UK, cephalopods such as octopuses are regarded as honorary vertebrates under the Animals Act 1986 and other cruelty to animals legislation, extending to them protections not normally afforded to invertebrates.
Read a lot more information about octopi here.