� When standing upright, the aliens are vaguely bipedal in form, though they adopt a more hunched, quadrupedal stance when walking or sprinting. They have a skeletal, biomechanical appearance and are usually colored in muted shades of black, blue or bronze. Aliens do not radiate heat, as their body heat matches the ambient temperature of the environment in which they are found. In most of the films, adult aliens have the ability of running and crawling along ceilings and walls. They have great physical strength, having been shown to be capable of breaking through welded steel doors, and matching Predators in single combat.
Aliens have segmented, blade-tipped tails. The sharp tip was initially a small, scorpion-like barb, but from Aliens onwards the blade design increased in size and changed in appearance to more closely resemble a slashing weapon. From Alien Resurrection onwards, the tails have a flat ridge of spines at the base of the blade. This was introduced to help them swim convincingly, and was left intact in the subsequent cross-overs. The original shooting script for Aliens and the novelization both featured a scene in which Lieutenant Gorman is "stung" by the barb tail and rendered unconscious. In the final cut of the movie, Gorman is knocked out by falling crates. As a weapon, the strength of the tail is very great, having been shown to be strong enough to impale and lift a Predator with seemingly little effort. They are also adept at using their tails as blunt weapons, sometimes to deadly effect, as seen in Alien.
They have elongated, cylindrical skulls but possess no visible eyes, though in the original Alien film, the top of the creature's head was semi-transparent, with empty eye sockets of human appearance visible within. This element was re-used for the "Predalien" 29 years later. How the creatures see is uncertain. In Alien 3, a fisheye lens was used to illustrate the alien's point of view. In the novelization of the movie Alien, the creature is held mesmerized by a spinning green light for several minutes. In Aliens, the adult creatures have a more textured head rather than a smooth carapace. In the commentary for Aliens, it was speculated that this was part of the maturation of the creatures, as they had been alive far longer than the original alien. The smooth design of the carapace would be used again in Alien 3 and Alien Resurrection, although made narrower with a longer muzzle and more prominent chin. This design would be kept in Alien versus Predator and abandoned in Aliens vs. Predator: Requiem in favor of the ribbed design. The aliens' inner jaws are powerful enough to smash through bone and metal.
Throughout their appearances, human spawned Aliens have been shown to have a fluctuating number of fingers. In Alien, the creature has webbed, six fingered hands. The number of fingers is reduced to three in Aliens, and are shown to be much longer and more skeletal. In Alien Resurrection, the number of digits is increased to four, with two long middle fingers and a pair of thumbs. This design is kept in the Alien vs. Predator films, though the hands were made bulkier in order to make the Aliens seem more formidable against the Predators.
Aliens have been alternately portrayed as both plantigrade and digitigrade organisms, usually in accordance to their host. Human spawned aliens were usually portrayed as having humanoid hind limbs, while in Alien 3, the featured Alien sported double-jointed legs due to its quadrupedal host. This characteristic would be continued in Alien Resurrection for the human-spawned aliens. Tom Woodruff, who had previously played the "dog-alien" in Alien 3, described the human spawned aliens in Resurrection as feeling more like a dog than the previous creature, despite having been born from human hosts. The human spawned Alien warriors would revert back to a plantigrade posture in Alien vs. Predator.
Alien blood is an extremely potent acid and is capable of corroding on contact almost any substance with alarming speed. It is dull yellowish-green in color, and seems to be pressurized inside the body so that it spurts out when punctured. Shusett suggested the idea that the creature have acid blood as a plausible means to make the creature "unkillable"; if one were to use traditional firearms or explosives to attack it, its blood would eat through the hull of the ship. The Alien novelization suggests that, at least at the "facehugger" stage, the acid is not blood but a fluid maintained under pressure between a double layer of skin. In later films in the series, the aliens are shown to be conscious of the effects of their acidic blood, and even use it to their advantage: In Alien Resurrection, two aliens escape a cage by killing a fellow alien so its acid eats through the cage floor; in Aliens vs. Predator a queen being held by chains apparently instructs several aliens to slash and cut her, thus corroding the chains. In the Aliens vs. Predator: Requiem documentary: "Science of the Alien", it is theorized that the aliens' acid blood could be some type of "hydrosulphuric acid" composition due to its corrosiveness and the conspicuously toxic effects on living human tissue. The documentary also speculates that Aliens are immune to their own acidic and toxic liquids due to a endobiological build-up similar to the human stomach's ability to protect itself from its digestive fluids. The documentary takes this theory one step further and speculates that the Alien organisms protection system against its own toxic hydrosulphuric acid is protecting the rest of the organism with what is basically a bio-organic produced teflon isolation.
Aliens can produce a thick, strong resin that they use to build their hives and to cocoon their victims, and they can use the walls of their hives as camouflage. They also salivate profusely. In the original Alien, the facehugger is shown to be able to "spit" acid, melting the faceplate of Kane's helmet and allowing the creature immediate access to the inside. This ability is also exhibited by adult aliens in Alien 3 and Alien Resurrection; much like a spitting cobra, they use it to blind and immobilize their victims.
Events on the LV-426 colony and USM Auriga showed that the species excels at observational learning and problem solving. In both cases, the aliens managed to learn how to operate the machinery of their mechanized environments at a very basic level. On LV-426, the aliens were able to cut the power from a section of the complex to allow themselves access to the humans. The queen was able to learn how to operate a giant elevator simply by observing it once. In the director's commentary for Aliens, James Cameron noted that the creatures in Aliens had been alive for far longer than the alien in the original, and so had more time to learn how to manipulate machinery. On the USM Auriga, they were able to use blood from another alien to melt through their enclosure and escape. With the exception of the "Newborn", Aliens have demonstrated little actual emotion, save for self preservation and maternal instincts toward their eggs.
They make few vocalizations beyond snarls and high pitched shrieks when in pain or attacking. They regularly hiss while active, but are otherwise silent, particularly when stalking prey.
Aliens are depicted as eusocial life-forms with a defined caste system which is ruled by a queen. Their life cycle comprises several distinct stages: they begin their lives as an egg, which hatches a parasitic larval form known as a facehugger, which then attaches itself to a living host by, as its name suggests, latching onto its face. The facehugger then "impregnates" the host with an embryo known as a chestburster, which, after a gestation period of several hours, erupts violently from the host's chest resulting in the death of the host. The chestburster then matures to an adult phase within a few hours, shedding its skin and replacing its cells with polarized silicon. Due to the transfer of DNA during the gestation period, the alien also takes on some of the basic physical attributes of the host from which it was born.
Ripley's first encounter with the QueenQueen aliens are significantly larger and stronger than the warriors, approximately 4.5� metres (15� ft) tall. Their body structure differs also, having two pairs of arms, one large and one small. The Queen's head is larger than other adult aliens and is protected by a large flat crest. Unlike other aliens, the Queen also has high heel protrusions from its feet. The Queen also seems to have increased intelligence compared to the other life-cycle stages, as the Queen on LV-426 was able to learn to operate an elevator. Pregnant alien queens possess an immense ovipositor on their lower torso, similar to a queen termite's, which is responsible for creating eggs. The queen is able to detach from the ovipositor. When attached to its ovipositor, the queen is supported by a "biomechanical throne" that consists of a lattice of struts resembling massive insect legs. Unlike insect queens, there appears to be no need for drones to fertilize an alien queen's eggs. The newest film installment, Aliens vs. Predator: Requiem also features a new form of oral implantation, by which the Predalien mimics the action of facehuggers, directly depositing multiple chestburster embryos into a host via its inner jaw. The Strauss Brothers, directors of the film, have gone on to say that this is a stage between queen chestburster and adult, in an attempt to build its army before it grows the egg sack and cannot defend itself.
In the initial cut of Alien, the alien possessed a complete life cycle, with the still-living bodies of its victims converted into eggs. However, the scene showing this final stage was cut for reasons of pacing, leaving the ultimate origin of the eggs obscure. This allowed Aliens director James Cameron to introduce a concept he had initially conceived for a spec script called Mother, a massive mother alien which laid the eggs and formed the basis for the aliens' life cycle. Cameron conceived the Queen as a monstrous analogue to Ripley's own maternal role in the film. In that vein, some critics have compared it to Grendel's mother.
The design of the queen was created by Cameron in collaboration with special effects artist Stan Winston, based upon an initial painting Cameron had done at the start of the project. The Winston Studio created a test foam core queen before constructing the full hydraulic puppet which was used for most of the scenes involving the large alien. Two people were inside working the twin sets of arms and puppeteers off-screen worked its jaws and head. Although at the end of the film the queen was presented full-body fighting the power-loader, the audience never sees the legs of the queen, save those of the small-scale puppet that appears only briefly. In Aliens, Cameron used very selective camera-angles on the queen, using the 'less is more' style of photography. Subsequently the movie won an Oscar for Visual Effects. An adult queen was to reappear in Alien Resurrection. The original mechanical head previously used in Aliens was provided by Bob Burns. It was repainted with a blend of green and brown, giving it a shimmering, insect-like quality. This color concept would be abandoned in Alien versus Predator in favour of the original black color scheme.
In the climax of the 2004 film Alien vs. Predator the queen's basic design was altered to make it more "streamlined" in appearance and its over-all size was increased to 6 meters (20� feet) tall. Other changes include the removal of the "high-heel" protrusions on its legs, including additional spines on its head and making its waist thinner because there was no need for puppeteers inside its chest. The animatronic laying queen had 47 points of hydraulic motion.
The eggs laid by the queen are large, ellipsoidal leathery objects about one meter high with a four-lobed opening at the top. As a potential host approaches, the egg's lobes unfold like flower petals, and the parasitic facehugger explodes from within. Giger initially designed the eggs with a much more obviously vaginal appearance, complete with an "inner and outer vulva". The producers complained that Catholic countries would ban the film if the allusion was too strong, so Giger doubled the lobes to four, so that, in his words, "seen from above, they would form the cross that people in Catholic countries are so fond of looking at." The interior of the original egg was composed of "Nottingham lace", which is the lining of a cow's stomach. The quick shot of the facehugger erupting from the egg was done with sheep's intestine. Initially the egg remained totally stationary save for the hydraulic movement of the lobes; however, by Alien Resurrection the entire egg was made to ripple as it opened.
The facehugger seen in AlienA facehugger is the second stage in the alien's life cycle. It has eight long finger-like legs which allow it to crawl rapidly, and a long tail adapted for making great leaps. These particular appendages give it an appearance somewhat comparable to chelicerate arthropods such as arachnids and horseshoe crabs.
The facehugger is a parasitoid; its only purpose is to make contact with the host's mouth for the implantation process, by gripping its legs around the victim's head and wrapping its tail around the host's neck. Upon making contact, the facehugger tightens its tail around the host's neck in order to render it unconscious through oxygen deprivation. The facehugger then inserts a proboscis down the host's throat, supplying it with oxygen whilst simultaneously implanting an embryo. Attempts to remove facehuggers generally prove fatal, as the parasite will respond by tightening its grip, and the facehugger's acidic blood prevents it from being safely cut away.
A facehugger has been observed shedding its cells and replacing them with polarized silicon in order to better survive in adverse environmental conditions. At least one facehugger has been shown to be capable of surviving exposure to the hostile environment of LV-426, where temperatures were cold enough to freeze carbon dioxide. Once the alien embryo is safely implanted, the facehugger detaches and dies.
Chestburster The chestburster that grew to be the adult in AlienAfter implantation, facehuggers die and the embryo's host wakes up afterwards showing no considerable outward negative symptoms. Symptoms build acutely after detachment of the facehugger, the most common being sore throat, slight nausea, increased congestion and moderate to extreme hunger. In later stages where the incubation period is extended in preparation of a queen birth, symptoms will include a shortness of breath, exhaustion, and hemorrhaging (detectable through biological scanners and present in nosebleeds or other seemingly random bleeding incidents), as well as chest pains inflicted either in lack of chest space due to the chestburster's presence, or even premature attempts to escape the host. The incubating embryo may take on some of the host's DNA or traits, such as bipedalism, quadrupedalism or possessing the mandibles of a Predator and other body structure changes. Over the course of 1–24 hours, indeterminable in some cases, and sometimes up to a week, in the case of some queens, the embryo develops into a chestburster, at which point it emerges, violently ripping open the chest of the host, killing it.
Aliens take on various forms depending on the characteristics of their hosts. Most of the aliens seen to date have been human-spawned, but a number of aliens born from other hosts have also been seen.
The quadrupedal Alien variant from Alien 3The "Dog alien" (also jokingly referred to as the "Bambi burster", or "Runner alien" in the expanded universe stories), was introduced in Alien 3. The creature itself shares the same basic physical conformation and instincts as the other aliens shown in the previous films, although there are several differences due to the host it was spawned from (a dog in the theatrical cut, an ox in the DVD assembly cut). The Dog Alien in its Chestburster form is a miniature version of the adult, unlike the larva-like human spawned chestbursters. The adult is primarily quadrupedal, has digitigrade hind legs and lacks the dorsal tubes of the human-spawned variety. This Alien is a skin included in the Game
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