Blood control

Blood control is a method of controlling an entity's actions via their blood - for example, a sample of A+ blood would allow a ship with sufficient technology to control all Humanity with A+ blood from the vicinity of Mars. However, blood control does have its limitations, like hypnosis, blood control could not be used to make a person commit suicide as the survival instinct is too great.

Not many races seem to have blood control, and the Doctor himself hadn't seen it in a long time, one example of a race with a capacity for blood control was the Sycorax, who would use the blood control as a bluff (if they could) to threaten to kill all the people on the planet affected if half the planet wasn't sold into slavery. (DW: The Christmas Invasion)

The Sycorax probably regarded blood control, like other technologies, as a form of witchcraft or sorcery.