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Cats are masterful predators, capable of spotting prey from meters away in the dead of night.
猫是娴熟的捕食者，能够在黑暗中发现数米外的猎物。
But place a treat in front of them, and they're basically blind. What's up with that?
但是对于面前的美食，它们基本就是个瞎子。这到底是怎么了？
How can such good hunters be so lousy at seeing what's right in front of them?
这么好的猎手，怎么就看不见眼前的东西呢？
It turns out that their vision isn't always amazing, since being able so see well at night comes with some drawbacks.
事实证明它们的视力时好时坏，能看清黑夜的同时也是有短板的。
Cats are crepuscular that means they're most active at dawn and dusk.
猫是在黄昏时候活动的动物，这意味着它们在昏晓时最为活跃。
As a result, their eyes have evolved to see best when the light is low. For one thing, their eyes are huge.
因此，它们的眼睛得到进化，在光线低沉时看的最清楚。首先它们的眼睛巨大。
They're nearly as large as human eyes, even though their heads are less than half the size of ours.
它们的眼睛几乎和人类的眼睛一样大，虽然它们的脑袋还不到人脑大小的一半。
Their slit-shaped pupils also have a greater range of size.
它们裂隙状的瞳孔大小范围更大。
Human pupils can dilate to 15 times their smallest size; cats' pupils can dilate by 135-fold,
人类瞳孔可以扩大15倍；猫的瞳孔可以扩大135倍，
and get even wider than human pupils to let in a lot more light.
为了看见更多的光，它们的瞳孔甚至可以张得更大。
The parts of their eyes that let in and focus light—their corneas and lenses—are also proportionally larger,
它们让光线进入和聚焦光线的眼睛部分—它们的角膜和晶状体—比例也更大，
which ultimately means more light reaches the light-sensing tissue in the back, called the retina.
这意味着更多的光可以抵达后边的感光组织—视网膜。
And they have an extra reflective layer behind their retina called the tapetum lucidum,
在它们视网膜的后边有一个额外的反射层—明毯，
which reflects back any light that reaches it, giving the retina a second chance to catch what it's missed.
可以反射任何光线，给了视网膜捕捉错失光线的第二次机会。
Special cells in the retina called photoreceptors are what actually sense light.
视网膜中感受光线的是特殊细胞—感光细胞。
And like us, cats have two types of photoreceptors: rods and cones. Rods work best in low light but don't sense color very well.
和人类一样，猫也有两种感光细胞：视杆细胞和视锥细胞。视杆细胞擅长低亮度，但不能很好的感知色彩。
Cones are used in color vision, but they only really work if there's a good amount of light.
视锥细胞被用于颜色视觉中，但它们只在光线充足的时候工作。
Cats have almost three times as many rods as we do, but only 10 percent as many cones.
猫的视杆细胞数量几乎是人类的三倍，但视锥细胞只有人类的10%。
That makes for killer night vision, but in bright light, those rods become overloaded and can switch off completely.
这有助于夜视杀手，但是在明亮的光线中，那些视杆细胞变得超负荷，且可以完全关闭。
That leaves the handful of cones to do the heavy lifting, which makes for pretty paltry daytime vision.
那些重活就留给了少数视锥细胞去完成，这有助于微小的白天视觉。
And those huge eyes? They're really hard to focus.
那么那些巨大的眼睛呢？它们其实很难聚焦。
To zero in on a nearby object, you need to bend that hard part of your eyeball, called the lens,
为了瞄准附近的物体，你需要弯曲眼球的晶状体，
enough to reshape how light enters your eye.
足够弯曲才能重塑进入眼睛的光线。
You have muscles in your eyes that can do that quickly when you need to focus on something close up.
你的眼睛里是有肌肉的，当需要聚焦近距离物体时，可以迅速弯曲晶状体。
But the massive lenses in cat eyes just aren't as flexible, so they don't bend as well as yours do.
但是猫眼睛中的巨大晶状体没那么灵活，所以它们不能像人类一样的弯曲。
Ultimately, this all means that cats simply can't focus on anything closer than about 25 cm to them.
最后，所有这一切意味着猫不能聚焦任何25厘米内的物体。
So when you hold a treat in front of kitty's face, all they see is a washed-out blur.
所以当你拿着零食凑到猫猫面前时，它们能看见的东西很模糊。
Luckily, their sense of smell is twice as sharp as yours. So if you hold that treat long enough, they're bound to sniff it out eventually.
还好，它们的嗅觉灵敏度是人类的两倍。所以只要时间够，它们能够闻到手中零食的味道。
Thanks for asking! And thanks especially to our patrons on Patreon.
感谢提问！特别感谢我们Patreon上的赞助人。
We cannot thank our community of patrons enough, as their continued support is what makes all that we do possible.
再怎么感谢我们社区的赞助人也不为过，因为他们的支持才有了我们的这一切。
If you'd like to learn how you can help us make educational science content like this video,
如果你想了解如何帮助我们制作像这样的有教育意义的科学视频，
or what being a patron is all about, you can head on over to Patreon.com/SciShow.
或是成为我们的赞助人，请移步Patreon.com/SciShow。
