Dolphins sleep with one eye open.

Each zebra has its own unique pattern of stripes.

A year on Mercury is just 88 Earth days long.

Stars twinkle because their light bends as it passes through Earth's moving air.

Your tongue print is unique, just like your fingerprint.

Rainbows are actually full circles — we usually only see half because the ground gets in the way.

Apples float in water because they are about 25% air.