The Slitheen are a fictional family of massive, bipedal extraterrestrials from the British science fiction television series Doctor Who and are adversaries of the Ninth Doctor and later Sarah Jane Smith. The Slitheen are of the egg-laying calcium-based Raxacoricofallapatorian race native to Raxacoricofallapatorius, though many use "Slitheen" in referring to the race in general. Instinctive hunters trained to kill at a young age, Slitheen are a ruthless criminal sect whose main motivation is profit. They are also convicted on their home world, not willing to return to their planet due to a death sentence. The Slitheen first appeared in the 2005 series episodes "Aliens of London" and "World War Three", and subsequently recur in later episodes of both Doctor Who and spin-off series The Sarah Jane Adventures. Physical characteristics Adult Slitheen are tall with overweight but muscular builds, long forearms, powerful sharp claws and baby-like faces. They have pairs of eyelids which move sideways, but have a nictitating membrane. They possess immense physical strength as they are strong enough to lift people off the ground and have a highly developed sense of smell, able to track a single target across a few city blocks, smell adrenaline and hormones in people, and can sense if one of their own dies. Female Raxacoricofallapatorians can produce poisons within their bodies to use against their enemies. Known methods of delivery include a poisoned dart that is formed in the finger and then fired, and exhalation of poisoned breath. Members of the Slitheen family have green skin, though there is variation in the skin tone of other Raxacoricofallapatorian families. In The Sarah Jane Adventures episode The Gift, members of the Slitheen-Blathereen family group are seen to have orange skin. The Slitheen disguise themselves by fitting into the skins of their victims, using compression fields created by a collar worn around their necks to squeeze their huge size into a slightly smaller space. Initially the compression ratio was limited, so the disguises tended to be obese people, though some disguises are also slim people. This issue was overcome by new technology by the time of The Lost Boy, in which the skins of thinner people were used (by the time of "From Raxacoricofallapatorius with Love" short people could also be used). The exchange of gases that compression entails also builds up within the acquired skin, causing very loud flatulence in humans (the expelled gas smells like