The human nose can distinguish more than 10,000 different smells.

There are hundreds of different kinds of neurons in the nose that specialize in recognizing different odors and transmitting those signals to the brain. This occurs when molecules of the things that you can smell travel to your nose. Whatever thing you are smelling (a flower, a piece of fruit, an onion, etc.) gives off light, volatile chemicals called odorants that make their way to your nose as they evaporate. These chemicals trigger the neurons in your nose that allow you to recognize the smell. Specialized smell neurons exist to pick up on different kinds of smells, allowing us to distinguish between over 10,000 different odorants.

 
Source: How Stuff Works

The average human heart beats 100,000 times each day.

All this expanding and contracting pushes around 2,000 gallons of blood through the human body! Over a 70-year lifetime, the average human heart will beat more than 2.5 billion times. If all our blood vessels were laid end-to-end, they would stretch for about 60,000 miles - circling the planet more than two times!

Source: American Heart

A man survived both the Hiroshima and Nagasaki atomic bombs.

Unfortunately, this remarkable individual passed away earlier this year at the age of 93. Tsutomu Yamaguchi is the only individual to be recognized as having survived both atomic bombs during World War II. Back in 1945, Yamaguchi was on a business trip to Hiroshima when the first bomb dropped on August 6th. The blast caused him to go blind and deaf temporarily, and had serious burns across his body.

He returned home to Nagasaki three days later to a second atomic bomb less than 2 miles from his house! The explosions caused him to go completely deaf in his left ear. In later years, he suffered from complications such as leukemia, cataracts, and other bomb and radiation-related illnesses. Yamaguchi was one of 200,000 Japanese citizens recognized as having been affected by either of the bombs.

The hardest part of the human body is the enamel that covers the teeth.

This is important because underneath the enamel in your teeth is a soft pulp made of connective tissue, blood vessels, and nerve fibers. Bacteria in your mouth can produce an acid that wears out your enamel. When the acids dissolves the enamel and gets to the nerves, you'll get a really nasty toothache.