It’s hard to believe something so colorful and playful could also be so distressing, but if you’ve ever stepped on a Lego brick with your bare foot, you’ll know there’s no pain quite like it.

So what makes these interlocking bricks of plastic such an unpleasant experience to step on?

This video from the American Chemical Society’s YouTube channel, Reactions, shows the science behind why these little Danish bricks really get your nerves zinging.

^{Main image credit: Frédérique Voisin-Demery/Flickr. (CC BY 2.0)}