Annoying eye twitches that make us feel self-conscious. Sleep twitches that refuse to let us sleep. Pins and needles that are just straight up weird.
We like to think that we’re in complete control of our bodies and that we understand it best. After all, every nook and cranny of the human body has been observed and studied for years — we must be experts by now, right?
A good portion of what goes on within us and why it happens remains a mystery and is often subject to debate.
Here are 6 strange involuntary bodily behaviours and their probable explanations:
(image url='http://static.businessinsider.com/image/5769a30491058427008ca928/image.gif' alt='Yawning' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a30491058427008ca928-1200/image.jpg')
We yawn when we're tired. We yawn when we're bored. Yawns are contagious.
But despite how often we do it, scientists aren't sure why we yawn. One idea outlined in a 2007 study is that yawning helps regulate our brain and body temperature. Our brains use more energy than any other human organ, which increases its tendency to heat up. When we stretch our jaws to yawn, blood flow is increased to the skull and, as we inhale at the same time, the air helps cool down the blood as it flows to our brains.
This suggestion could also help explain why we yawn more as we get ready for bed or while we are getting up in the morning -- our body temperatures are at their highest points during these times and yawning helps us cool down.
(image url='http://static.businessinsider.com/image/5769a1f791058422008ca759/image.gif' alt='Hiccups' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a1f791058422008ca759-1200/image.jpg')
Hiccups are repetitive and involuntary spasms of your diaphragm, a muscle located below your lungs that regulates your breathing. It contracts when you inhale and relaxes as you exhale. When the diaphragm falls out of its normalized rhythm, you get the hiccups (medical term: singultus).
Each contraction of the diaphragm causes the larynx and vocal cords to close, resulting in a rush of air into the lungs as you gasp or make the well-known 'hic' of a hiccup.
Hiccups can be caused by overeating, eating or drinking too quickly, eating spicy food (which can irritate the lungs and stomach), swallowing too much air, and drinking carbonated beverages (which can irritate the nerves in our esophagus).
(image url='http://static.businessinsider.com/image/5769a47f52bcd01b008cad12/image.gif' alt='Pins and needles' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a47f52bcd01b008cad12-1200/image.jpg')
If you've ever crossed your legs for too long, you know the feeling: A numbing, prickly, burning sensation. That pins-and-needles feeling is caused by extra pressure being placed on a nerve (medical term: parathesia).
The pressure reduces the blood supply that normally gets sent to a given area and prevents nerves from sending the right signals to your brain. Once the pressure is lifted, the nerves can work properly again -- though they are misfiring as they get back to normal.
Long-term pins and needles may be an indication of a wide variety of other health conditions like diabetes, carpal tunnel syndrome, or traumatic nerve damage.
(image url='http://static.businessinsider.com/image/5769a184910584e73c8ca699/image.gif' alt='Eye twitch' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a184910584e73c8ca699-1200/image.jpg')
Whether it's your eyelid or the area below your eye, an involuntary spasm in the eye area is relatively common.
There are a number of causes of eye twitches -- including stress, fatigue, lack of sleep, and too much caffeine -- and depending on the cause, they can last for anywhere from a few seconds or minutes to a few months. While they may be annoying, keep in mind that these twitches are pretty harmless and eventually go away on their own.
(image url='http://static.businessinsider.com/image/5769a4ad52bcd01b008cad14/image.gif' alt='Sleep twitch' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a4ad52bcd01b008cad14-1200/image.jpg')
Also known as a hypnagogic jerk or a sleep start, the hypnic jerk is an involuntary muscle spasm or falling sensation that commonly occurs as you fall asleep.
Scientists think hypnic jerks happen as a result of the conscious brain handing over its 'duties' to the unconscious body. During this transition, the brain steadily slows down its release of serotonin which, on top of making us feel good, helps control the larger muscles in our body so we don't move around too much in our sleep. When you feel a sleep start, your body is entering REM sleep, but hasn't fully paralysed itself yet.
(image url='http://static.businessinsider.com/image/5769a4df52bcd0210c8cabc1/image.gif' alt='Light sneeze' link='lightbox' size='secondary' align='right' nocrop='true' clear='true' jpg='http://static.businessinsider.com/image/5769a4df52bcd0210c8cabc1-1200/image.jpg')
The 'photic sneeze reflex,' also known as the Autosomal Cholinergic Helio-Ophtalmologic Outburst (ACHOO), is characterised by a sneeze or prickling sensation in the nose after direct exposure to intense bright lights like the sun. It affects about one in every 4 people.
Though the exact cause has not been pinpointed yet, scientists believe it's a result of high-sensitivity to visual stimuli and messy cross-talk between two nerves: The optic nerve and the nerve that usually triggers a sneeze.
NOW WATCH: Briefing videos
Business Insider Emails & Alerts
Site highlights each day to your inbox.