Octopus arms have a mind of their own. Two-thirds of an octopus’ neurons reside in its arms, not its head. As a result, the arms can problem solve how to open a shellfish while their owners are busy doing something else, like checking out a cave for more edible goodies. The arms can even react after they’ve been completely severed. In one experiment, severed arms jerked away in pain when researchers pinched them.