What's the joke about penguins hitting peas?

A scientist went to the South Pole and met a group of penguins. He asked one of them, "What do you do every day?" Penguin said, "Eat, sleep and beat peas." He asked the other, "What do you do every day?" Penguin also said, "Eat, sleep and beat peas." He asked many penguins, and they all said, "Eat and sleep and beat peas."

Later, he met a little penguin, very cute, and asked him, "What do you do every day, little friend?" The little penguin said, "Eat and sleep." The scientist was stupefied and immediately asked, "Why don't you hit peas?"

The little penguin said, "Because I am a bean."