Although we are constantly using it, many of us actually know very little about our bodies. We've been told that it allegedly takes more muscles to frown than to smile. We’ve also learned in school that we are born with 270 bones but only have about 206 during adulthood. Here’s some mind-boggling facts about unknown body parts, some of which are all but useless and others that have only recently been discovered.

Arrector pili

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You know when you are feeling aroused, excited by music, extremely cold, or perhaps frightened and your hairs stand on end? Well, there’s a little muscle at the base of every hair follicle that contracts and forces them to rise. Scientists have discovered that these muscles are leftovers from when we were furry homo sapiens. Way back when, the arrector pili helped our ancestors to raise their fur in order to stay warm in colder climates and make themselves appear larger in the face of adversity. For most of us the activation of the muscle is involuntary, but there have been reported cases of controlled goosebumps.

Auricular muscles

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They are of little use to humans and, without prior knowledge, it’s unlikely that you’ll be able to see or feel them, but on our outer ear are three muscles called the auricular muscles. In other mammals, such as bats, cats, dogs, and horses, they serve to move the ear towards sounds. One of the three muscles controls the upward and forward movements, another raises it, and the other pulls it backwards. About 10-20% of the human population have ear-wiggling capabilities, which is thought to be hereditary. That’s not to say that you can’t teach yourself.

Interstitium

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For centuries scientists believed that our organs were surrounded by a wall of collagen. That was until 2018, when an investigation discovered that everything inside of us—blood vessels, digestive tract, lungs, the lot—has fluid-filled cavities all around it. These cavities make up one enormous organ and are a vital component of the immune system. The name interstitium comes from the interstitial fluid that it contains. Simply put, the cavities protect anything that needs shock absorption in our daily lives.

Lacrimal punctum

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Otherwise known as the eyelid hole, the lacrimal punctum are minuscule holes found on the eyelids. To be more specific, they are located at the extreme inner corners of the upper and lower eyelids. Their purpose is to drain tears from our eyes to our nose, which is why we sometimes get a runny nose when we cry. Curious to see what they look like? Get up close to a mirror, push your eye’s lower corner upward and look for often barely visible holes.

Plantaris

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Running down the back of our leg is a thin muscle called the plantaris that measures about 10 centimeters in length. Together with the plantaris tendon, it forms the longest tendon in the body. Bizarrely, it has been reported absent in 7 to 20% of cases. Consequently, some say that it is a vestigial muscle, while others suggest that it is necessary for supporting motion in both the ankle joint and knee. You might find out if you ever rupture it while playing basketball, soccer, or tennis.