Yawns have to be one of the most powerful forces in the universe. They’re just as contagious when you’re face-to-face with someone yawning as they are during a Zoom call with a person halfway across the planet. I can personally attest to yawning while on the phone with somebody who yawned in another state. Now, researchers have discovered that yawns are so contagious that when a pregnant woman yawns, the fetus inside her may yawn too.

According to a study published in Current Biology, scientists found evidence suggesting fetuses can “catch” yawns from their mothers while still in the womb.

Researchers at the University of Parma in Italy tested the idea by showing yawning videos to 38 pregnant women during their third trimester. Cameras recorded the mothers’ reactions while ultrasounds monitored fetal movement. About 64 percent of the women yawned at least once after watching the videos. Of those cases, just over half of the fetuses yawned roughly 90 seconds later.

Scientists already knew fetuses yawn naturally during development. Those fetal yawns are believed to help prepare the muscles and neurological connections involved in breathing and facial movement. But researchers previously thought prenatal yawning was a biological function and not the more behaviorally linked, socially contagious thing we know it can be. And honestly, they still aren’t entirely sure what triggers a fetal yawn.

But why are fetuses copying their mothers’ yawns?

One theory is that it’s more of a mechanical thing, with the physical movement of the mother’s yawn creating pressure changes in the uterus that trigger a yawn in the fetus. Another idea involves hormones or neurological synchronization during pregnancy.

It’s anyone’s guess right now, and it’s a mystery that we may have to wait a long time to answer, since there are more pressing yawn-related mysteries to solve, like why we even yawn in the first place, because we still haven’t quite figured out that part yet.

Again, there are theories. Scientists think it might have something to do with regulating brain temperature. It could also be the body’s natural way of maintaining alertness when you’re sleepy. It could be the synchronized social behavior we all know it to be. And then, asked why it’s contagious, we also aren’t sure, but we do know that it’s been observed in humans, dogs, lions, and birds, too.

We don’t know much about yawning, and every time we do learn something new, it only reveals how deep the mystery of the yawn truly goes. So while he may not understand it, just know that if you’re a pregnant woman, every time you yawn, your unborn child might be yawning along with you.