Catch their yawn,
love them more?

The full narration of the video.

You let out a big yawn on the couch. A few seconds later, your partner yawns too. Next to a stranger on the subway, usually nothing. People online say: if your yawn spreads to someone, they care about you. That's only half true.

First, the yawn itself: mouth wide open, a deep breath in, then slowly out. Why do we do it? The best-known idea: it cools the brain. Opening wide speeds up blood flow in the head. The cool air carries a little heat away.

In Arizona, researchers watched 80 people in winter and 80 in summer. Nearly half yawned in winter; fewer than a quarter in summer. Summer air there is about body temperature, so it cools nothing. Another idea: yawns help the brain shift gears. Just woke up, nearly asleep, bored stiff: that's when they come. Neither idea is settled.

Yawns also spread. When someone yawns, it's like passing you a ball. Yawn back, and you've caught it. Take a guess: when a stranger yawns, how many times out of ten do you yawn too? Italy's University of Pisa watched people at meals, at work, on trains: 109 adults, for a whole year.

A stranger's ball: caught less than once in ten. An acquaintance's: just over once. A friend's: about three times. Family and partners: five. And the closer you are, the faster you catch it. Is it just because you keep looking at the people you love?

In 2020, they picked out nearly 300 yawns that were heard but not seen. Back turned, sound only, family and friends still spread it most. So, is it the love hormone? There's one called oxytocin, nicknamed the cuddle hormone. In one US experiment, 60 male students got a nasal spray: half got oxytocin, half a fake, then they watched yawning videos.

The oxytocin group didn't yawn more. Instead they covered their mouths and clenched their jaws to hide it. So 'closer means catchier' is an average over lots of people. As a test for the two of you, it doesn't work. Duke University showed 328 people yawning videos: about one in three never yawned at all. And the older you are, the less you catch them.

If your partner doesn't yawn back, maybe they're on their phone, wide awake, or just not a catcher. One missed ball doesn't mean you're not a team. Even dogs play favorites: in a Japanese study, dogs yawned back at their owners more than at strangers. Tonight, when your partner's sleepy, give them a big yawn and count the seconds. No reply? Pass a few more. Come back and tell us how many seconds it took.