Read the clue description first.
The octopus clue is an electromechanical device that uses a microcontroller and custom-built driver circuits to drive five solenoid actuators in patterns which correspond to text. The electronics were housed in a plexiglass case, which was housed in a drainage box from Home Depot. Here's how it was built:
Octo-Plexiglass box was designed in CorelDraw (pic), and cut using a lasercutter.
Octo-Solenoid driver boards were generated by the PCB utilities in Protel, and cut from copper-coated board with a Roland Modela tabletop milling machine. The interesting part of the circuit is the DRV101 (PDF) chip from Burr-Brown, which takes care of supplying current and driving the solenoids in a pulse-width-modulation fashion so that they don't burn out. Backside | see-through of one board | another see-through of one board
Octo-Electronics were driven by a PIC16F876 microcontroller, which was actually a bit of overkill for the needs of the device. The octopus sensed when a hand was inside by a magnetic switch connected to a flap that gets pushed over by the hand. Have a look at the circuit soup.
Octo-Power for the solenoids was provided by 4x6V lantern batteries, hung in the rafters of the octopus using cable-ties. The 5V sensing and control circuit was powered by a separate 9V battery run through a 7805 voltage regulator. See the mounting scheme.
the Outside of the Octopus was made with a drainage container from Home Depot. The mouth was coated with gaffer's tape in order to prevent hands from being harmed as they entered the mouth. The acrylic box was attached to the grated platform (which goes underneath the big box) with cable-ties (pic). Cable-ties also held the grated platform to the big box.