You’re sitting across from your significant other at dinner and let a huge yawn escape. A few seconds later … nothing. They don’t yawn back. Is that a red flag?
We’ve all heard that yawning is contagious—but does it go deeper than that? It does according to science writer Sam Kean. Humans “don’t pick up contagious yawning until 4 or 5,” he writes in his upcoming book The Tale of the Dueling Neurosurgeons, “implying that we need to develop certain parts of the brain first, probably related to social skills and empathy.”
He may be on to something. Research at the University of Pisa discovered that your yawn is especially contagious if you yawn in front of close relatives like parents, siblings and children. But as day-to-day familiarity and empathy decline, so do returned yawns. When you yawn around close friends, the number of yawns you’ll get back goes down. And the numbers dwindle even more in front of strangers, with your yawn losing most of its contagiousness.
Timing is also important—the research found that yawns are returned more quickly the closer you are to someone. Kean even wonders “if you could tell someone was falling out of love with you by timing their yawn delay.” Well, perhaps, but if you’re starting a stopwatch every time you yawn in front of your partner, perhaps things aren’t going so well in the first place.