B.F. Skinner performed a classic experiment on pigeons, providing them with an intermittent reward (a grain of bird seed) to peck at a button. By slowly increasing the interval between rewards, he was able to train a pigeon to peck at the button 10,000 times before receiving the reward.

So, what could be the reward for this bird, that he bangs into a window thousands of times? Is there such as thing as a bird masochist?