Electricity is all around us. It’s in the wires in our walls, and in the atmosphere. It’s in our phones, our cars, and, these days, our books. But it’s also hiding in a very unexpected place: our bones.

It’s called piezoelectricity, which translates to “electricity by pressing or squeezing.” Brothers Paul-Jacques and Pierre Curie—yes, that Pierre Curie—first coined the term to describe the electricity they saw in compressed quartz and tourmaline crystals.

Basically, piezoelectricity is a way of converting mechanical energy into electricity. Pressure disrupts the balance of an object’s electrical charges. One side of a crystal takes on a positive charge, and the other side becomes negative, which makes it a sort of microscopic battery.

This doesn’t work on everything (stop squeezing your cat, please), only certain crystals. But you’d be surprised how many things those crystals make up, and how useful they can be. 

Piezoelectricity is the force that allows voice recognition software to turn sound waves into signals your computer can use. It’s the reason quartz watches are so accurate, and the force that transforms the grooves on a vinyl LP into music we can hear. We can thank piezoelectricity for cigarette lighters, microphones, gas grills, ultrasound technology, and even potato guns. But its effects don’t stop with appliances; piezoelectricity has been found in all kinds of organic materials, from silk and wood to arteries, tendons, and bone. 

Yes, you have crystals in your bones. Our skeletons are made of both hard and soft tissue. The rigid parts that hold us up are composed of crystals of calcium phosphate, also known as bone salt.

Japanese scientists first found evidence of piezoelectricity in human bone in the late 1950s. In the nearly six decades since, their experiments have been replicated and their results validated. Our bones definitely can hold a charge—and that works to our advantage. 

As it turns out, bone responds pretty well to a little jolt of electricity. Electrical stimulation encourages bones to grow and heal, a fact that’s now being exploited by orthopedic surgeons. Our bones are living, changing objects, endowing the body electric with their odd little spark.