Sometimes the human body is astounding. It can pull trucks, carry quintuplets, run ultra-marathons, and climb Mt. Everest. But then, just when we think we’ve hit the pinnacle of achievement, we get ouchies when we eat a bowl of ice cream too fast.

These moments remind us we’re still ordinary animals, who for one reason or another find meaning in scaling mountains and then climbing back down, before resuming our daily lives. But sometimes the weird and strange aspects of our bodies don’t seem so bad when we understand what’s going on. Here are six physical responses that actually have pretty normal explanations.

1. Butterflies

It’s five minutes before a class presentation and you’ve just realized you put your underwear on outside your pants. (Classic you.) You were already nervous about speaking in front of everyone; now you have a second problem to deal with. You get that terrible sinking feeling, and a swarm of butterflies rustles in your gut. You know this is bad.

Your brain knows it, too. Thousands of years of evolution have programmed your parasympathetic nervous system to respond to any major threat, even non-threatening ones, as if it were the end of the world. A signal in your kidneys releases adrenaline and the blood leaves your digestive system. That’s the sinking feeling: the moment the blood leaves your stomach. Your brain decides you don’t need digestion anymore, because you should either be fighting or fleeing — not giving a presentation in your Spiderman undies.

2. Charlie Horse

Muscle knots, known more formally as trigger points and colloquially as Charlie horses, aren’t technically knots (or horses). But in that godawful moment of searing, intolerable pain, who really cares if they’re a knot or not?

These “knots” are long, involuntary contractions that occur in specific muscle regions. They pull on either end of the muscle, which causes you pain until you can massage it out or wait for the contraction to end. Usually, they won’t result in any real damage like permanent tears. Some people may experience more knots than others because of underlying diseases that impair their overall muscle function.

3. Seeing Stars

Imagine how many stars you’d see if you got knocked out beneath the clear and cloudless sky of the American Southwest. The answer is a lot. Unfortunately, you wouldn’t get a very clear look at the celestial bodies because the pressure on your optic nerve would obscure your vision.

When we see stars, typically as a result of some heavy force hitting our heads, the “light” we perceive is actually a collection of phosphenes, the phenomena of seeing light when none enters our eye. It results from the optic nerve’s signal to the retina, which has the dumb property of either seeing light or not. This explains why rubbing your eyes early in the morning can produce the same effect as a haymaker in Flagstaff.

4. Pins and Needles

Your nerves are kind of high-maintenance. You can’t put them under too much pressure, or else they won’t work right. The problem is we can’t be held accountable when we’re asleep and sometimes we have the tendency to roll over onto our limbs. Enter: pins and needles.

A limb waking up from its own solitary slumber is rarely fun. You feel the shooting prickly sensation of pins and needles (known in science talk as paresthesia) because the nerves that had temporarily quit sending signals to your brain are now getting kicked into high gear. Blood rushes back to the site, and capillaries refill. “Pins and needles” is what nerves feel like when they transition from an inhibited to working state.

5. Brain Freeze

If only bodybuilders could work out their trigeminal nerves, they might not fall to the crippling pain of overzealous ice cream eating. A brain freeze, or ice cream headache depending on your vernacular, originates when the nerve that runs from the roof of your mouth, throughout the middle of your face, and ultimately to your brain, tells blood vessels to rapidly constrict and expand.

If you’ve ever been told to press your tongue to the roof of your mouth, that’s why it works. The heat from your tongue quiets the nerve’s cold response, letting the blood vessels freely expand. And since the trigeminal nerve handles facial pain, your brain confuses the pain’s origin (i.e. your mouth) with how that signal travels through your head, making your forehead the unlucky scapegoat.

6. Growling Stomach

Unlike a lot of medical jargon, the real word for a growling stomach — borborygmus — is more fun than the slang. It actually refers to the noise produced by a process called peristalsis, in which the intestines push fluid and gas through the body. Doctors can listen to the sound with a stethoscope, but if you’re particularly famished the noise will be audible because there are more empty spaces for the sound waves to pass through.

This, of course, makes a growling stomach something of a red herring — it’s your intestines making the fuss. But the stomach does play a role, particularly when it’s empty, by sending a signal to the brain to jumpstart peristalsis. The vibrations that propagate through your digestive tract (alongside some key hormone releases) help trigger hunger, which means you and your stomach can complain together.