Have you heard the phrase “chew on this”? Literally, it means to crush something with your teeth. Figuratively, it means to contemplate. Some curious scientists combined these meanings, as they thought about the role of chewing in humankind’s evolution.

Chewing, they suspected, uses a small but significant amount of your daily energy. So, to put their money where their mouths were, the researchers ran an experiment. They put participants under a clear ventilated hood—like a fishbowl with two plastic hoses. This hood measured the oxygen a participant breathed in and the carbon dioxide they breathed out, allowing the scientists to discern how much energy was expended during a task, otherwise known as the metabolic rate. Each participant then chewed gum.

Here’s another phrase you might know: “He can’t walk and chew gum at the same time,” meaning that someone is generally inept. After all, it seems that neither activity takes much effort. The scientists, though, discovered that we don’t give mastication enough credit. When participants chewed soft gum, their metabolic rate rose 10 percent. When they chewed stiff gum, their metabolic rate rose 15 percent. In other words, though humans only spend about 35 minutes a day chewing, even a modest change in food’s properties—like its softness or stiffness—changes the energetic costs.

While our ancient ancestors weren’t measuring their metabolic rates with bubble gum, they were likely putting in a fair bit of effort to chew raw food. As humans evolved, our food softened, thanks to processes like cooking and agriculture. Consuming softer food means less energy expended—and might have allowed humans to evolve our current facial structures.