A greeble or nurnie is a small piece of detailing added to break up the surface of an object to add visual interest to a surface or object, particularly in movie special effects. They serve no real purpose other than to add complexity to the object, and cause the flow of the eye over the surface of the object to be interrupted, usually giving the impression of increased size. It is essentially the small detailed technical part of a larger object. The detail can be made from geometric primitives, including cylinders, cubes, and rectangles, combined to create intricate, but meaningless, surface detail. Greebles are commonly found on models or drawings of fictional spacecraft in science fiction.
An early physical example of their application was in the production of the spaceships in 2001: A Space Odyssey (1968) where they were called "wiggets". Another first recorded use of the term was by those working on the special effects for Star Wars - the group who would later become Industrial Light and Magic. They also described this design method as "guts on the outside".
In physical models, these greebles could be anything from parts of plastic cut to an interesting shape, or actual elements taken from shop bought model kits. For instance, in Star Wars the original Imperial Star Destroyer was constructed from a plywood frame and adorned with sheet styrene. Panel lines were cut into the sheet styrene, but essentially that left the ship looking extremely bare. Hundreds of model kits were purchased and the model department promptly took pieces of the model kits and cut them up and stuck them along with more sheet styrene to the surfaces of the ship. The ultimate effect was to make the ship appear more believable to the viewer through the addition of these large areas of ancillary details. The nurnies themselves served no purpose other than to fill space and individually had no definite function to the design of the ship. Although later each nurnie was given a specific function by either fans or technical illustrators for fan guides.
Another example of nurnie application was the Battlestar Galactica model for the original seventies series which featured on its hull pieces of Apollo rockets, Saturn rockets and F16 fighter jets with oodles of bits of model tank kits to name a few.
As would be expected, given these origins, greebling is most commonly associated with the particular kind of large city-like spaceships made popular in Star Wars, but has been generalized to refer to any dense covering by different (usually mechanical) components. Similarly, Borg ships (and drones) in Star Trek appear heavily "greebled".
An anecdote from the creation of the first Star Wars movie involves the Tunisian customs enquiring what part of the costume of C-3PO (listed as "assorted greebles") was. Their response was allegedly "Something that looks cool but doesn't actually do anything." Most of the weapons carried in Star Wars were replicas of common World War II firearms with "extra" vents, scopes and other unneeded pieces added on.
Ron Thornton is widely believed to have coined the term "nurnies" referring to CGI technical detail that his company F.I. produced for the Babylon 5 series.
In 3D computer graphics, greebles are often created automatically by specific software, because generating greeble involves a lot of precise, tedious, and repetitive work, and many consider it a task best suited to computers, particularly if a great degree of control is unnecessary or the greebles will not be particularly large on screen. Most greeble generating software works by sub-dividing the surface to be greebled into smaller regions, adding some detail to each new surface, and then recursively continuing this process on each new surface to some specified level of detail. Similar algorithms are used in the creation of fractal surfaces.