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It may have happened when you locked eyes with your secret crush, or before an important job interview, but what exactly caused that strange, fluttering sensation in your stomach?

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Maybe you're checking your phone, wrapped up in your own world, and then suddenly you make eye contact with your crush sitting across the coffee shop or you're headed into an interview for a life changing job oppourtunity or you're filming a video that's going to be watched by hundreds of, thousands of people!

Before you know it you start to feel that fluttering in your stomach. Butterflies.

We all know that insects don't spontaneously grow in our guts. So where does that feeling come from? Look no further than the autonomic nervous system or ANS.

It's a part of your nervous system that is found outside of your brain and spinal cord. Your autonomic nervous system is responsible for bodily functions that you aren't conscious of like pumping blood, breathing, and digesting food. And the ANS can be split into two main branches, the parasympathetic and the sympathetic nervous systems.

The parasympathetic nervous system helps create a mellowed-out state of "rest-and-digest". Your heart rate slows, blood vessels dilate, pupil size decreases, and muscles in your gastrointestinal tract relax. On the flip side the sympathetic nervous system is responsible for that "fight-or-flight" response you've probably heard of.

Thanks to this branch you're prepared for stressful or potentially dangerous things. Like imagine human ancestors out hunting hundreds of thousands of years ago knowing all the time that they were also prey. After all there were bear-sized hyenas roaming around.

Thankfully you don't really have to worry about being eaten by hyena-bear anymore but your bodies response isn't all that different when you run into a crush or perform in front of a crowd it's just to a lesser degree. Your heart rate still increases, your airways and pupils dilate, your stomach muscles begin to contract, and you start breathing more heavily to prep for uncertainty. Will I say something stupid?

Do I look ridiculous? How does my breath smell? A surge of hormones, like adrenaline, accompany this response they redirect blood away from the stomach, where you don't need extra blood flow in times of danger, to other muscle groups.

Your leg muscles, for example, need all the oxygen and nutrients they can get cause they help you kick hyena-bears, or run away from them as quickly as possible. Adrenaline also affects how your gut muscles contract, and scientists think that's partially what causes that tense, squirmy feeling. Also, there are millions of sensory nerves in your stomach that detect a sudden decrease in oxygen as the blood rushes away, which could be another source of that butterfly-like flutter.

So whether it's a first date or a frantic search for a misplaced wallet just remember, evolution prepared you for this moment. Badly. Thanks for watching this episode of Sci-Show if you want to keep learning about all kinds of science with us from the human body, to actual butterfly metamorphosis you can go to to subscribe