The Kantrofarri also known as Dream Crabs are the main antagonists of the Doctor Who 2014 Christmas Special Last Christmas.They are crab-like alien parasites that feed on humanoid brain matter. Due to being blind and deaf, they hunt by using telepathy to pick up the perceptions of themselves in people's minds. Kantrofarri would then ambush their victims from above, latch themselves onto their face and pacify them by placing them within a telepathically induced dream state. The creatures would then drill into their victim's right temple and slowly liquefy the contents within for consumption.
In order for the victim to get a Kantrofarri off them is to realise that they are dreaming. In turn, the creature could further attack them within the dream and place them within mutible layers of dreams to make it more difficult to escape. If a person was successful to wake up, the Katrofarri would then disintegrate.
They are a homage to the Xenomorph during their "Face-Hugger" state, made infamous in the Alien franchise.