Think of a bodily function—one you perform maybe half-a-dozen times a day, but without choosing to or even really understanding why. Hint: it is considered inappropriate to do this at the dinner table on a first date.
If you thought of “yawning,” congratulations on taking the high road and pegging what behavioral researcher Robert Provine calls “the least understood, common human behavior.”
Seriously: despite boatloads of research into the subject, nobody really knows why humans yawn or what precisely triggers one. We yawn when we’re bored, but also when we’re stressed. We let loose a gaping yawn when we’re tired at the end of the day, and when we’ve just awoken refreshed from the night’s sleep. We yawn when we see other people yawning, and even when the family dog swings loose his slobbery jowls to suck in some fresh air in anticipation of a walky.
And oddest of all, if you read the last paragraph intently, there’s a 55% chance that you yawned just from reading about yawning.
It’s bizarre, but true. Researchers discovered as much in an infamous Temple University study that found students forced to read about yawning yawned nearly twice as much over a 30-minute period as students who read about itching, or nothing at all. Yawning is such a powerfully empathetic behavior that even just reading about it (and therefore thinking about it) can trigger a yawn.
Professor Provine, a contagious behavior wonk who literally wrote the book on yawning, sees the humble yawn as one of the ultimate expressions of human empathy. Why? Nobody knows. Yawning is often correlated with stretching, and linked with movement immediately after; perhaps a yawn is a way to relax us and those around us, or maybe a symbolic call to action.
Whatever the case, if this story didn’t get your facial muscles flexing, fret not: there is no such thing as a perfectly contagious yawn. Across dozens of trials that exposed participants to various expressions of yawning—including footage of a giant gape, a close-up mouth, and even just asking students to think about yawning—Provine was never able to find a yawn that got more than 55 percent of witnesses to yawn back. Even if you’re a scientist, it seems, you can’t force people to yawn. (But here are the jokes scientists use to test intelligence.)