Ao1 - The chain of causation must create a direct link between the D;s actions and the result. Factual causation is based on the 'but for test' (but for D's actions would have V survived) this can be seen in R v White. Legal causation means that d's acts must be the 'operative and substantial' cause of harm, as in R v cheshire. Also, important the thin skull rule, D cannot reply on the deficiency in the victim to escape liability, as shown in r v Blaue, where D could not escape liability the victim refused blood transfusion due to religious reasons.