It took place in the 1960s - when a lot of strange things took place. It was an experiment where some scientists placed some dogs in a cage, the floor of which was wired to generate an electric current. The scientists locked these dogs in the cage and then they activated the current. It was strong enough to shock the animals, but not to injure them. Needless to say, every time the electricity went through that cage floor, the dogs jumped around and yelped in pain - for a while. It wasn't too long before they got used to the shock, and their only reaction was just a slight twitch. At that point, the scientists opened the door of the cage. But when they turned on the voltage, the dogs just took the shock again - not one of them got out, even though the door was wide open. Now, they had been hurt so many times, they were just conditioned to it. The final step in the experiment was to send a dog into the cage who had not been conditioned to that voltage. As soon as the current went through the cage, that new dog yelped and made a mad dash out the door of the cage - followed by all the other dogs.