YouTube user Corroder666 has recreated a moving, twitching Frankenturret from Portal 2.
Using a combination of cubes modeled with wax and lined with silicone, Photoshop and an incredible amount of effort, the designer of the replica was able to recreate the Frankenturret — a hybrid of the weighted companion cube mixed with two Sentry Turrets. In the video above you can see how the replica turret even moves.
A short overview of how the Frankenturrent was designed is available here, although be warned it won't be of much use for non-German speakers.