Why do chickens shake their heads while running?

Have you ever watched a chicken run? Did you norice how it shake its head? Scientists now know the secret of this problem.
They took slow-motion pictures of a chicken’s running and studied the picture carefully. They found out that the chicken’s head did not move back and forth. It only jerked forward – then the body caught up. And when its eyes was covered, the head couldn’t jerk anymore.
The scientist had found out that the chicken only jerk its head forward to see better. Wouldn’t it be funny if most chickens needed glasses.