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Why does nails on a chalkboard give you chills?

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📓 The short answer

Nails on a chalkboard sound awful because our ears naturally amplify those frequencies. It's theorized that we evolved this sensitivity to better detect the warning calls of our primate ancestors.

📚 The long answer

Hearing nails scraped on a chalkboard is a truly awful sound. For the masochists reading this, have a whirl and click on the video below.

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Nails on a chalkboard is rated as one of the most hated sounds in the world (in case you were wondering, the sounds of vomiting, microphone feedback, and crying babies are the top three.) Let's dig into why researchers think this sound is so horrible to listen to.

One reason the sound of nails on a chalkboard feels so intense is that the human ear naturally amplifies those frequencies (thanks, ears). The graph below shows how our threshold for hearing mostly lowers as the frequency of a sound increases. Interestingly, we become the most sensitive to sounds between 2,000 and 5,000 Hz (see the bump between the red arrows).

We're particularly sensitive to these frequencies because the shape of the outer ear boosts sound waves in that range. Why? Well, that's where we don't have all the answers, but we do have a theory.

As it turns out, the sound waves of nails on a chalkboard are strikingly similar to that of a chimpanzee scream. Both fall between 2,000-5,000 Hz.

From an evolutionary standpoint, it makes sense that our ears would naturally resonate with the frequency of a chimpanzee scream. If we can hear our fellow chimpanzee call out to let us know about a potential threat, we can escape.

This primal theory gained more credibility when a 2012 fMRI study found that sounds in this range (specifically testing nails on a chalkboard) activated the amygdala, the part of the brain responsible for triggering our fight-or-flight fear response.

So the next time you hear nails being scraped on a chalkboard, you can be grateful that the only threat you face is auditory discomfort and not a lion threatening to eat you and your chimpanzee family.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

🌐 Wikipedia article of the week

​Lace card​

"A lace card (also called a whoopee card, ventilator card, flyswatter card, or IBM doily[citation needed]) is a punched card with all holes punched. They were mainly used as practical jokes to cause disruption in card readers. Card readers tended to jam when a lace card was inserted, as the resulting card had insufficient structural integrity to avoid buckling inside the mechanism."

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👀 Catch up on other curious questions

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• ​What causes the "butterflies in your stomach" feeling?​​
• ​How does lightning work?​​

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