One night, when Henry got home and flipped on the light switch, the kitchen exploded, leaving him severely injured. The explosion was caused by a failure of the gas connector, which allowed a large amount of gas to escape, and a small spark created by turning on the light caused it to explode. Henry sued the gas corporation, arguing that it knew the connection was defective but it did not warn its customers. Henry won the case. He is most likely to have won the lawsuit on the grounds of: