Ood

The Ood, also known as Oodkind, were a gestalt species of telepathic humanoids native to the Ood Sphere. Humanity enslaved the Ood, mutilating them to ensure a dedication to servitude.

The Ood were a humanoid species with tentacles used for feeding purposes located on the lower portions of their faces. They had no vocal cords and instead communicated by telepathy. The Ood had long lifespans; Ood Sigma lived 100 years after the human enslavement ended and the Tenth Doctor was surprised at this, thinking he should have been much older. (TV: The End of Time)

The Ood had two brains: a forebrain in the head and a secondary hindbrain. The hindbrain was usually held in their hands, and was connected by an umbilical cord-like connection to their faces. The forebrain did much of the thinking and stored the telepathic sensors. The hindbrain processed memory and emotions, leading to mental instabilities when removed. The Ood could survive with it being removed and replaced with the more commonly seen translation sphere that connected to an Ood's nervous system. (TV: Planet of the Ood) The Ood Elder had a larger, external forebrain (TV: The End of Time). A giant Ood Brain located on their home planet acted as their telepathic centre; if the brain was destroyed, it would kill the entire species, and if suppressed the mental capacity of the species would be severely weakened. (TV: Planet of the Ood)

Under normal circumstances the Ood were gentle and harmless creatures. However, due to their brain structure they were susceptible to corruption, as demonstrated by how easily the race was enslaved by Ood Operations. (TV: Planet of the Ood) More worryingly, their passive telepathy allowed them to be easily controlled and/or possessed by more powerful telepathic entities, such as the Beast (TV: The Impossible Planet) and House. (TV: The Doctor's Wife)