Glass frogs have the rare ability to turn on and off their nearly transparent appearance, researchers report Thursday in the journal Science. Ernesto Benavides/Getty Images Now you see them, now you ...

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 ...

Now you see them, now you don't. Some frogs found in South and Central America have the rare ability to turn on and off their nearly transparent appearance, researchers report Thursday in the journal ...