Active euthanasia is death is brought about by the addition of a particular action (e.g., injecting with a substance meant to stop a body system from functioning), as opposed to passive euthanasia when death results from the removal of a life-sustaining process (pulling the plug on a ventilator). Active euthanasia involves the stopping of some already functioning body system. If the patient is breathing on their own, intentionally doing something to stop the breathing is an example of active euthanasia. If the patient is not capable of breathing and a ventilator is removed, the breathing would cease on its own, and thus removal is passive euthanasia rather than active euthanasia. Controversy surrounds situations in which a patient seeks out someone to provide active euthanasia. Due to complicated ethical considerations regarding the mental status of the patient making such a request, as well as beliefs stemming from some faith systems, disagreement exists in whether or not it is considered murder.