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If it hasn't been said to you, you've probably heard it on TV or in a movie:
如果没人告诉你的话，你可能也从电视或电影里听过：
Stay calm around strange dogs because they can smell fear,
在不熟悉的狗狗身边要保持镇定，因为它们能够闻到恐惧，
and they might attack, but until recently scientists hadn't looked to see if that was true.
而且它们可能会攻击你，但是直到最近科学家们才去验证这是真是假。
Now we know that they can smell fear, but when they do, they don't get aggressive, they actually get scared too.
现在我们知道它们是可以闻到恐惧的，但是当它们闻到恐惧的时候并不会攻击你，它们也会害怕。
Dogs have amazing noses. Their sense of smell is 10 to 100 thousand times better than ours,
狗狗们的鼻子让人惊异。它们的嗅觉是人类的10到100倍，
which is why they can help us detect traces of chemicals from bombs, drugs and even people buried under the snow.
所以它们能够帮助人类探测炸弹、毒品甚至埋在雪地里的人的痕迹。
That's thanks to the sheer number of olfactory receptors they have. Up to three hundred million, compared to our measly six million.
这是因为它们有绝对数量的嗅觉感受器。和人类稀疏的六百万相比，它们可有三亿个。
And to the fact that, relative to their size, the part of their brain that analyzes smells is about 40 times the size of ours.
由于狗狗的体积，它们用于分析气味的大脑部分是人类的四十倍。
But even so, dogs don't rely entirely on their sniffers.
但即便如此，狗狗也不是完全依赖于它们的嗅探器。
When they want to communicate with each other or with us, they usually can use body language and vocalizations as well.
当狗狗想和其他狗狗或者人类交流时，它们通常也可以使用肢体语言和声音。
When we tell them they're such a good doggo,
当我们夸狗狗时，
they process the tone of our voice and the words that we're speaking in different brain areas just like we do when other humans talk.
它们可以处理我们在不同大脑区域发出的声音和词语的音调，就像我们人类间的彼此交流一样。
Which means they do understand what we're saying to some extent, and we know that dogs are good at picking up on physical signals.
这意味着从某种程度上来讲，它们确实理解我们所说的话，并且我们知道狗狗可以很好的领悟身体信号。
In fact, studies have shown that they can differentiate between our emotions based off of our faces and body language.
事实上，研究表明它们可以基于我们的面部和身体语言区别我们的情绪。
So for a while, most scientists and dog trainers figured that dogs don't need to sniff out our feelings, they can see it in our posture and hear it in our voice.
所以多数科学家和驯狗师认为狗狗不需要嗅出我们的情绪，它们可以从我们的姿势看到，从我们的声音里听到。
It wasn't until recently that researchers looked directly into whether dogs can smell fear.
直到最近研究人员才直接调查狗狗是否能够闻到恐惧。
When we're afraid, the sweat we produce contains different chemicals than when we're happy or sad.
害怕时，我们产生的汗液比开心或悲伤时所产生的汗液包含更多不同化学物质。
Because the composition of our blood changes in response to hormonal signal.
因为我们血液的成分随着荷尔蒙信号发生改变。
So scientists can stick swabs in our armpits while inducing different emotions, and then to see how dogs react to those odours.
所以当我们出现不同情绪时，科学家可以在胳肢窝戳一只棉签，然后拿去观察狗狗对这些气味的反应。
And they did this in a 2016 study published in Behavioural Brain Research,
在2016年的一项研究中，他们做了这个实验并发表于《行为大脑研究》，
and then found that dogs' heart rates increased when they sniff sweat from people who watch a scary video, suggesting that they can smell fear.
他们发现当狗狗闻到那些看恐怖片的人流出的汗液时，它们的心率上升，这表明它们可以闻到恐惧。
But the animals had the same reaction to sweat from people who worked out, so it wasn't clear if they were just sensing physical arousal.
但是动物对运动留下的汗液也有同样的反应，所以还是不清楚它们是否只是感觉到了身体兴奋。
Then a study in Animal Cognition in 2017 did a similar experiment.
然后2017年《动物认知》做了相同的实验。
They had dogs sniff pads with sweat from people who watched scary or happy videos or unused pads,
他们让狗狗嗅那些看恐怖片或娱乐视频的人在平板电脑上留下的汗液以及未被使用过的平板电脑的味道，
but this time the researchers watched the dogs' behaviour afterwards and looked at heart rates.
但这一次研究人员观察狗狗之后的行为并观测心率。
The dogs that smelled the happy sweat were friendlier to strangers, their heart rates were generally higher than the control's,
闻过开心汗液的狗狗对陌生人更加友好，它们的心率普遍比对照组要高，
but lower than the dogs that had sniffed the fearful sweat.
但是比那些闻恐惧汗液的狗狗要低。
Meanwhile, the dogs that smelled fear seemed stressed out, seeking more reassurance from their owners,
同时，闻到恐惧汗液的狗狗似乎很紧张，想向它们的主人寻求更对安慰，
and acting more wary of new people, and like the previous study their heart rates went up.
对陌生人也更加谨慎，就像之前的实验一样，它们的心率上升。
So the researchers concluded that the dogs were detecting emotions, and reacting by feeling a similar way.
所以研究人员总结到狗狗能探测情绪，并通过感受一种相似的方法做出反应。
Sniffing joy put them in a better mood, and the smell of fear didn't make them more aggressive, it scared them.
闻到开心让它们心情更好，闻到恐惧并没有让它们更具攻击性，只是会吓到它们。
So it seems like dogs can potentially smell fear and know how you're feeling, but rest assured the feeling will probably be mutual.
所以似乎狗狗可以闻到恐惧，也知道你的情绪，但是毫无疑问这种情绪是相互的。
Thank you for asking, and thank you especially to our Patreon President of Space SR Foxley.
感谢提问，特别感谢我们的赞助人，Space的总裁 SR Foxley。
Thank you, SR for help and make Scishow possible. If you want to support this show head on over to patreon.com/scishow.
谢谢SR的帮助我们才能制作科学秀。支持我们，登录patreon.com/scishow。
