Second unit is a discrete team of filmmakers tasked with filming shots or sequences of a production, separate from the main or "first" unit. The second unit will often shoot simultaneously with the other unit or units, allowing the filming stage of production to be completed faster. Function The functions of the second unit vary, but typically the first unit films the key face-to-face drama between the principal actors. Two frequent ways a second unit is used are: Action sequences: Action sequences are often filmed in discrete locations, using stunt performers, rather than the principal cast, and requiring significantly different filming arrangements than for ordinary scenes. Therefore, they are an opportunity for second unit shooting. "Pick-ups": After the main unit has finished on a set or location, there may be shots that require some or all of this setting as background but that do not require the principal actors. These shots may include things such as close-ups, inserts, cutaways, and establishing shots. In both of these scenarios, the purpose of the second unit is to make the most efficient use of some of the resources that are expensive or scarce in film production: actors' and directors' shooting time, sound stage usage and the cost of sets that may have been built on stages. The work of second units should not be confused with multiple-camera setups, where several cameras film the same scene simultaneously. Large productions may have multiple second units. Although filmmakers may refer to having "three or four units working", each unit would be called an "additional second unit"; usually none would be described as the third or fourth unit. Directors The second unit has its own director and cinematographer. A key skill for a second unit director is to be able to follow the style being set by the film's primary director. Peter MacDonald, second unit director on X-Men Origins: Wolverine, The Bourne Ultimatum, and Harry Potter and the Goblet of Fire, has said, "The most important thing about any second unit is that you can't tell the difference between the second unit and the first unit. It must have the stamp of the first unit, both in photography and the style of direction. ... You try to copy what the first unit does as much as possible. You mustn't be on an ego trip and try to do your own style, because your material has to cut