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. These yawns ...

What if you had the power of invisibility, but it only works when you’re asleep? That might be useful for a surreptitious nap in public, but it still probably wouldn’t suit you as well as it does the ...

As tiny glass frogs fall asleep for the day, they take almost 90 percent of their red blood cells out of circulation. The colorful cells cram into hideaway pockets inside the frog liver, which ...