Orb (The Satanic Mill)
From Tardis Wiki, the free Doctor Who reference
The Orbs were mechanised spheroidal guards used by the Eleven aboard the stellar manipulator. They were tasked with monitoring the workers and killing those who were no longer able to work. The Eighth Doctor and Liv Chenka destroyed a number of Orbs using the sonic screwdriver, although it took time to do so. (AUDIO: The Satanic Mill)
