What activities give rise to strict liability and what defenses are available to strict liability?

Strict liability, or liability without fault, arises from
(a) performing abnormally dangerous activities,
(b) keeping animals, and
(c) selling defective, unreasonably dangerous products. Abnormally dangerous activities are those that
(a) create a foreseeable and highly significant risk of physical harm even when reasonable care is exercised by all actors and
(b) are not a matter of common usage. Examples include blasting, crop dusting, drilling for or refining oil in populated areas. Trespassing animals or any action by a wild animal generally causes strict liability for the owner. Merchant sellers and manufacturers who sell goods in a defective condition unreasonably dangerous to the user or consumer are held strictly liable. Contributory negligence is not a defense to strict liability. However, comparative negligence is available in some states for some types of strict liability. Express voluntary assumption of risk is also a defense to strict liability.