Octopus are carnivorous marine mollusk, which eat small crabs and scallops, plus some snails, fish, turtles, crustaceans (like shrimp), and other octopuses.
They catch prey with their arms, then kill it by biting it with their tough beak, paralyzing the prey with a nerve poison, and softening the flesh. They then draw out the flesh. Octopuses hunt mostly at night. Only the Australian Blue-ringed octopus has a poison strong enough to kill a person.
Their radulas are extremely efficient tools for aiding eating of these organisms, especially for penetrating a thick mollusk shell or arthropod skeleton. The octopus will grasp the organism and drill a tiny hole with their radula and using their salivary papilla insert a paralyzing toxin which relaxes the organism allowing their shell or exoskeleton to be penetrated (Fiorito and Gherardi 1999).
Although most Octopuses look friendly and cute, and small ones probably are, there are also giant octopuses to consider. Although it is very rare, if you are in the water which they call home, they may attack. This could be because they want to eat you, or simply because they would like a hug.
Either way, it is a good idea to be prepared. Here are some tips on how to detach them and escape from their clutches shared by Quirkbooks.com.