You know the feeling. It’s getting close to bedtime, you get sleepy, and you start yawning automatically. You may even find yourself yawning in the middle of the day in a mid-day lull.

His work Bronx Zoo shows a cheetah resting on a yellow pole and yawning heartily, its body patterned with tags and symbols - including the logo of the "Campaign for Nuclear Disarmament". The name of ...