You've operated one your entire life, but the human body still keeps secrets. See how well you know the hardware.
How many bones are babies born with, compared to adults?
Around 300, fusing down to 206 by adulthood.
Which bone are humans born without?
The kneecap — it starts as cartilage and ossifies over several years.
What is the body's largest organ?
The skin — about 8 pounds and 22 square feet on an adult.
What is the strongest muscle by force relative to size?
The masseter — your jaw muscle.
How much of the human body is water?
Roughly 60% in adults.
Which body part never stops growing subtly with age?
Ears and noses — cartilage keeps changing and gravity does the rest.
How fast is a sneeze?
Up to about 100 mph.
What is the smallest bone in the body?
The stapes, in the middle ear — about the size of a grain of rice.
How strong is stomach acid?
Strong enough to dissolve zinc — your stomach lining replaces itself every few days to cope.
How many miles of blood vessels are in the human body?
Roughly 60,000 miles — enough to circle Earth more than twice.
Which organ can regenerate a large portion of itself?
The liver — it can regrow from as little as a quarter of its mass.
How many cells are in the human body, roughly?
On the order of 37 trillion.
What percentage of your body's energy does the brain consume?
About 20%, despite being roughly 2% of body weight.
Do humans really lose most body heat through the head?
No — that's a myth from a flawed 1950s military experiment. Heat loss tracks exposed surface area.
Between the self-replacing stomach lining and the regrowing liver, the maintenance schedule you never see is the most impressive thing you own.
