The next time you make popcorn, you're watching thousands of tiny pressure explosions.

Each popcorn kernel contains a small amount of water trapped inside a hard outer shell. As the kernel heats up, that water turns to steam. But the shell is so tough that the steam cannot easily escape.

Instead, pressure builds.

Inside the kernel, the pressure can reach about 135 pounds per square inch (psi) before the shell finally ruptures. That's roughly four times the pressure inside a typical car tire and significantly higher than the pressure inside a champagne bottle.

While all of this is happening, the starch inside the kernel softens into a hot paste. When the shell finally bursts, the trapped steam expands almost instantly, causing the starch to inflate and explode outward.

The fluffy white popcorn you eat is actually the inside of the kernel turned inside out and frozen in place as it cools.

Not all corn can do this. Popcorn comes from a special variety called Zea mays everta. The name everta comes from a Latin word meaning "to turn inside out," which is exactly what happens when a kernel pops. Most other types of corn crack or leak steam before enough pressure can build.

Humans have been enjoying this natural trick for thousands of years. Archaeologists have discovered ancient popcorn remains in the Americas, showing that people were popping corn long before the arrival of Europeans.