Barnett v Chelsea and Kensington Hospital Management 
Three walk-in male patients attended Accident and Emergency Department but the medical officer just dismissed them. Later, one of them died of rare arsenic poisoning. This is a case about 'causation', whether the discharge of the patient leads to his death or not.
Judgment held: 'But for' even admitted there was little chance or no chance that the only effective antidote would have been administered to the patient in time. Although the hospital had been negligent, because it was more likely than not that he would have died anyway, the negligent was not the cause of his death.
Be careful! Something really rare does happen in our daily practice!