4 is the only number in English which is spelt with the same number of letters as the number itself!
The Earth weighs around 6,600,000,000,000,000,000,000 tons (5,940 billion billion metric tons)!
Cats have over 100 vocal sounds, while dogs have only about 10
The placement of a donkey's eyes in its head enables it to see all four feet at all times!
The average person sees over 1,460 dreams a year!
The penguin is the only bird that can swim, but not fly!
There is zero gravity at the center of the Earth
Fingernails grow 4 times faster than toenails!
Human teeth are almost as hard as rocks!
Algebra, Trigonometry and calculus came from India.