1. Most people dream in black and white.

2. Deaf people use sign language in their sleep.

3. Humans are the only mammals that willingly delay sleep.

4. Two third of a cat's life is spent asleep.

5. Sleep boost immunity.

6. Our sense of smell decrease when we are sleeping.

7. Elephant sleeps less than human.

8. Tigers and infants sleep the same amount.

9. Male and female circadian rhythms are slightly different. 

10. Humans can sleep with their eyes open.