Neil Fraser made this Portal Pumpkin to guard his home for Halloween 2010. You can peek inside at the mechanism that made it move and scare the living daylights out of trick-or-treaters.
Perched precariously on its three legs, the turret automatically pans left and right and pitches up and down searching for targets. Inside is a small motor and a system of gears and cams to drive the gun mounts.
He said it was like building a ship in a bottle- "A wet, slimy bottle." Link -via reddit