Goosebumps, chill bumps, whatever you call them, you know what they are – they appear all over your skin when you’re cold, but also when your hackles are raised against a threat, real or perceived.

For most of us, this reaction is completely involuntary, and even surprising. But for a small subset of folks, goosebumps are something they can experience whenever the mood strikes.

When Travis Carrasco was a child, he had what his parents considered to be an odd habit of swaying his head back ad forth. When they asked him about it, he said he was giving himself goosebumps. They didn’t believe him, but now, the successful 29-year-old engineer from Las Vegas, Nevada knows he wasn’t imagining it – and he’s not alone.

Scientists believe that about 1 in every 1500 people have what they’ve termed Voluntarily Generated Piloerection (VPG) – the ability to give themselves goosebumps. But even though they have a name for it, neuropsychologists everywhere are intrigued but perplexed by the ability, which flies in the face of our previous understanding of the unconscious nervous system.

Goosebumps arise when tiny muscle, connected to a hair follicle, contracts. The hair stands, the skin around it undergoes a bump-shaped distortion, and there you go. The muscle is called the arrector pili – a smooth muscle that, like the others in the body, is believed to be unconsciously regulated, since the nerves attached to them exist in the autonomic nervous system. The autonomic nervous system is full of bodily functions we’re not meant to control, because they need to happen automatically – things like heart rate, pupil dilation, and digestion.

Which is why when James Heathers, a physiologist at Northeastern University, was completely intrigued the first time he read about it in an engineering paper. He told Mental Floss…

“That was catnip for me. VGP shouldn’t be possible. That’s not how the autonomic nervous system works; what it does. This reason that it’s called autonomic – autonomous – it means ‘without thought.'”

Though Heathers’ specialty lies in data science and electronic health development, he dove into the phenomenon and authored a paper in 2018. For it, he sifted through obscure internet forums and sent out survey, which resulted in 32 participants with the ability.

32 participants who, according to Heathers, share some personality traits.

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“They seem to be more creative; they imagine more. They pay more attention to themselves. They track their emotions more closely. They have a preference for new stuff…That’s either an artifact of people who are more open being more likely to answer a survey on the internet for fun, because they want to know about themselves, or it’s a component of the experience itself.”

If you’re thinking that you, too, could give yourself goosebumps by focusing on a sound or visual, like fingernails scratching a chalkboard, Heathers says that’s not the same thing.

“VGP has no mental or cognitive component. The vast majority of people who do it, in the way that we’ve defined it, simply have a really straightforward pathway. A lot of the time, they focus on a point, behind their ear or on their neck or at the back of the head. They don’t have to think of anything.”

So, they only picture getting goosebumps, not something that would give them involuntary ones.

Carrasco, the little boy whose parents surely thought him imaginative and a little odd, explained how he does it to Mental Floss. 

“Basically, it starts at the base of my neck, the bottom of my head and the backside. When I trigger it, it feels like a bunch of sparks travel throughout my entire body, and I can do it repetitively, over and over and over and over and over. However, the strongest sensation is only the first couple times.”

Since he was a child, his process has been to sway his head from side to side.

“It’s a weird rhythm, but if I sway my neck, it triggers a really strong response. You know hen you squeeze your eyes really tight, and sometimes you hear pressure building, and it’s really just squeezing a muscle in your ears or your eyes. It’s similar to that, but when the goosebumps happen, sometimes I can hear that same pressure…it feels relaxing. It feels good.”

Though Carrasco and people like him consider the ability an odd sort of sixth sense, the truth is that scientists don’t really understand it at all. It might have a genetic component and it might not, but with so few people to study, we might never know for sure.

Just something to think about the next time goosebumps break out over your flesh.