This picture got me thinking.
It shows the reaction of some of the Dutch Royal Family when the car crashed into their parade (story here)… you can see they’ve covered their mouths in a common reaction to shock.
Why do we do this? It’s seems almost to be a reflex action, but I can’t see what benefits it brings from an evolutionary perspective… maybe because when shocked we breathe in sharply to get as much oxygen into the bloodstream, and it stops us inhaling insects / dust etc?
IAMNABiologist, but I doubt that humans have such a specific reflex action. The evolutionary reflex action seems to be the more general “flood the system with adrenaline for fight or flight”, but what to do with this adrenaline is an individual reaction to a specific problem.
I guess that the cover-your-hand reaction is more a learned response.
Note that it is the norm in many places to cover your mouth when you open it wide. That includes yawning and in some places even when laughing. So you have shocked -> mouth open -> hand covering. It soon becomes a reflex to cover your mouth even if it isn’t open when you are shocked or surprised.
Agree. I don’t think it’s the mouth covering that’s reflexive. It’s the mouth opening, and in a lot of cultures, we are taught to cover our open mouths.
C&P from another thread, but I think it applies here, too:
Desmond Morris believes that people touch their own faces in times of stress as a comforting action. In the absence of someone else (like a parent) holding the person, the person in a sense is trying to hold himself/herself.
But that’s just one person’s opinion.
Because it’s rude to show your gaping mouth at someone.
Cicadas.
In evolutionary terms, people standing around in shock failed to notice cicadas flying into their mouths and subsequently choked to death. People who covered their mouths survived the occasional cicada, and their genes became dominant.
It just doesn’t seem like a conscious action though. Maybe it’s just very ingrained? But I don’t recall ever being “taught” to cover my mouth when shocked in the same way as yawning and sneezing?
I often yawn without covering my mouth, and sneezing if I’m alone. But even when I’m alone or not really paying attention and see something really shocking I’ll raise a hand to my mouth… I think the Desmond Morris idea has some merit, lots of people play with their lips when they are nervous or upset.
I was gonna go with bees, but otherwise it sounds about right 
Presumably only every 17 years…
I don’t know about the open-mouth thing. I noticed myself doing it one time when I’d been shocked–I didn’t open my mouth, but my hands flew up to my face instinctively, fingertips on my mouth, fingers covering my chin. I thought it must be some primal comfort gesture.
I could see the benefit of stifling any uncontrolled noise should our caveman ancestors get startled or shocked by a lion or bear, say.
Any chance it’s related to that “soul escaping through your mouth” notion mentioned here?
(hijack – just in case readers are unaware, there are peiodic ciadas on shorter cycles and there are annual cicadas which appear every year.) Aside from that nitpick, the joke is good. Carry on. 
I believe it’s an evolutionary thing to hide your teeth so that it doesn’t look like you’re showing your fangs to someone you didn’t intend to show them to.
I doubt that – smiling seems to counter this.
The self-comfort thing makes sense. It isn’t just horror that people tend to do this during – it seems to be any sudden surprise, doesn’t it?
I agree. I’m far more likely to bring my hand up to a closed mouth when shocked - or concerned, in which a similar but gentler gesture occurs. In fact, it’s almost like my fingers hold my mouth shut, as if to maintain my speechlessness. But it’s probably closer to a need for comfort, almost like holding your arms to your chest.
So… kind of like we shocked/frightened and instinctively move to suck our thumbs?
i thought it was a smother the scream thing. don’t want the bad thing to hear you.
Ive never done this and Ive never seen anyone do this in real life. I doubt its biological. It a learned behavior exaggerated in hollywood for dramatic effect.
