Eggshell skull

The eggshell skull rule (or thin-skull rule) is a legal doctrine used in both tort law and criminal law that holds an individual liable for all consequences resulting from their activities leading to an injury to another person, even if the victim suffers unusual damages due to a pre-existing vulnerability or medical condition. The term implies that if a person had a skull as delicate as the shell of an egg, and a tortfeasor or assailant who did not know of that condition were to tap that person on the head, causing the skull to break, the responsible party would be held liable for all damages resulting from the wrongful contact, even though they were not forseeable. The general maxim is that the defendant must "take their victim as they find them".

The doctrine is applied in all areas of torts - intentional torts, negligence, and strict liability cases - as well as in criminal law. There is no requirement of physical contact with the victim - if a trespasser's wrongful presence on the victim's property so terrifies the victim that he has a fatal heart attack, the trespasser will be liable for the damages stemming from his original tort. The foundation for this rule is based primarily on policy grounds. The courts do not want the accused to rely on the victim's own vulnerability to avoid liability.

The case of Smith v. Leech Brain & Co., 2 QB 405 (1962), illustrated this rule. An employee in a factory was splashed with molten metal, as a result of the burn he developed cancer and died. The defence argued that he may have had a pre-existing disposition to cancer. However, the judges dismissed this on account that such circumstances were irrelevant.

In 1891, the Wisconsin Supreme Court came to a similar result in Vosburg v. Putney, 80 Wis. 523, 50 N.W. 403 (Wis., 1891) (reversed and remanded for a new trial on other grounds). In that case, an eleven year-old boy kicked a 14 year-old boy in the shin while at school. It turned out that the 14 year-old was recovering from a previous injury. The kick resulted in the boy entirely losing the use of his leg. No one could have predicted the level of injury before the kicking. Nevertheless, the court found that since the kicking was unlawful, as it occurred during school and not on the playground, the 11 year-old boy was liable for the injury.

Crumbling skull

A defense against the eggshell skull rule is the crumbling skull rule. The rule rebuts the eggshell skull by arguing that whatever harm incurred by the vicitim was inevitable and the defendant's acts only had a minimal effect upon the already deteriorating circumstances. For example, a dying patient is treated improperly by a doctor. Though the doctor did more harm than good, he cannot be held liable for the death of the patient because of the crumbling skull rule.

The crumbling skull rule can be seen as denying causation rather than rebutting the eggshell skull rule itself. In crumbling skull cases, it generally cannot be argued that, but for the defendant's actions, the harm to the victim would not have occurred.