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.