Octopus bimaculoides, the California two-spot octopus. (Cassady Olson) Their arms are capable of making decisions independently and can even continue to react to stimuli after being severed.

The inner workings of octopus arms might seem a world away from everyday human life, but there’s a surprising amount of real-world utility to this research.

As you collect materials, think about whether they’d work underwater, where octopuses live. To create your den, start by ...