In behavioral psychology, extinction is the termination of a reinforcement. Tests performed on pigeons show that extinction of a reward result in frustration - two pigeons were placed in a cage, one of them tethered to the rear wall, the other one free to walk about and reach the food-dispensing mechanism. Every 30 seconds, the dispenser would provide food for the free pigeon. When this stopped, the free pigeon would attack the innocent bystander - the tethered pigeon, who had nothing to do with the food-dispensing and the termination thereof.