Edward Thorndike’s research with cats in puzzle boxes broadened the theory of associative learning by introducing the notion of consequences to associative learning. Thorndike expanded the notion of associative learning beyond instinctual behaviors and sensory substitution to genuinely novel behaviors. Thorndike’s experiments initially probed, e.g., how cats learned to lift a lever to escape the “puzzle boxes” (the forbearer to “Skinner boxes”) that they were trapped in. The cats’ behaviors, such as attempting to lift a lever, were not themselves instinctual behaviors like the URs of Pavlov’s experiments. Additionally, the cats’ behaviors were shaped by the consequences that they brought on. For Thorndike it was because lifting the lever caused the door to open that the cats learned the connection between the lever and the door. This new view of learning, operant conditioning (for the organism is “operating” on its environment), was not merely the passive learning of Pavlov, but a species-nonspecific, general, active theory of learning.