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Cat person？ How many pictures of your cat sleeping have you got on your phone？ A lot， right？ They are so cute when they sleep...so cute. But then they are always asleep. Okay， not always， but a lot of the time. Why is that？
The truth is that cats sleep an average of 15 hours per day. Some of them stretch that toward 20 hours， especially older cats and kittens. That’s understandable. What’s wearing out the rest of them？
Cats are natural predators1. Their prey2 is quick and elusive3. Sneaking up and pouncing4—repeatedly—is undoubtedly exhausting. Cats in the wild work hard in order to meet their food needs， and expending that kind of physical effort requires a lot of recharging.
And they are not just predators， they are crepuscular5 predators， which means that the go lights come on for them at dawn and dusk during the twilight hours when their prey—rodents6 and birds—are equally active. The rest of the day， cats sleep， though that sleep is of two types.
About three fourths of their sleep is a shallow7， almost-waking rest. Cats doze in a kind of ready position. Their senses of smell and hearing are in the “on” mode. Ears occasionally twitch8. Peaceful but poised9， they are ready to react instantly： To pounce on prey or to swat and scratch the hell out of you for the temerity10 of petting them while they are sleeping. It usually lasts 15 to 30 minutes.
The other one fourth of the time， cats really sleep deeply. If it looks like they are dreaming when their paws tremble， it is because they probably are dreaming.
So what about my domestic， never-leaves-the-house cat？ Why is she always sleeping？ In a word： Heredity11. As a species， cats—whether they sleep on the street or on a sofa—are all hardwired12 to the same internal clock. That， and house cats also sleep when they are bored.
你是愛猫人士吗？你的手机里有多少张猫睡觉的照片？很多，对吧？它们睡觉的时候很可爱……很可爱。但是它们总是睡着的。好吧，不说总是，但很多时候都是。为什么会这样？
事实是猫平均每天睡15个小时。它们中的某一些把这个时间延长到了20个小时，特别是年龄更大的猫和小猫。这是可以理解的。但是什么让其他的猫也精疲力竭呢？
猫是天生的捕食者。它们的猎物动作又快又难以捉摸。悄悄靠近，再猛扑过去——反反复复地——这毫无疑问是累人的。野猫为了满足食物的需要而努力捕食，而消耗了这种体力则要补充大量的精力。
它们不仅仅是捕食者，它们是晨昏性捕食者，这意味着，在天微亮的黎明和黄昏时分，当它们的猎物——啮齿动物和鸟类——同样活跃时，它们的出行信号灯就会亮起来。一天里的其余时间，猫会睡觉，不过它们的睡眠有两种类型。
它们四分之三的睡眠是浅层的，几乎是醒着的。猫以一种预备的姿势打瞌睡，它们的嗅觉和听觉处于“开启”模式，耳朵偶尔会抽动一下。它们平静而沉着，随时准备做出反应：猛扑猎物，或者因为你在它们睡觉的时候鲁莽轻拍，而将你拍打抓挠得屁滚尿流。这种浅眠通常持续15到30分钟。
另外四分之一的睡眠时间里，猫真的睡得很沉。如果它们的爪子抖动看起来像在做梦，那是因为它们可能就是在做梦。
那我家里从不离开屋子的猫呢？为什么它总是睡觉？简言之，是因为遗传。作为一个物种，猫无论是在街上睡觉，还是在沙发上睡觉，都有同一个基本固定的生物钟。因此，家猫也会在无聊的时候睡觉。
（英语原文选自：www.britannica.com）
【Notes】
1. predator [
The truth is that cats sleep an average of 15 hours per day. Some of them stretch that toward 20 hours， especially older cats and kittens. That’s understandable. What’s wearing out the rest of them？
Cats are natural predators1. Their prey2 is quick and elusive3. Sneaking up and pouncing4—repeatedly—is undoubtedly exhausting. Cats in the wild work hard in order to meet their food needs， and expending that kind of physical effort requires a lot of recharging.
And they are not just predators， they are crepuscular5 predators， which means that the go lights come on for them at dawn and dusk during the twilight hours when their prey—rodents6 and birds—are equally active. The rest of the day， cats sleep， though that sleep is of two types.
About three fourths of their sleep is a shallow7， almost-waking rest. Cats doze in a kind of ready position. Their senses of smell and hearing are in the “on” mode. Ears occasionally twitch8. Peaceful but poised9， they are ready to react instantly： To pounce on prey or to swat and scratch the hell out of you for the temerity10 of petting them while they are sleeping. It usually lasts 15 to 30 minutes.
The other one fourth of the time， cats really sleep deeply. If it looks like they are dreaming when their paws tremble， it is because they probably are dreaming.
So what about my domestic， never-leaves-the-house cat？ Why is she always sleeping？ In a word： Heredity11. As a species， cats—whether they sleep on the street or on a sofa—are all hardwired12 to the same internal clock. That， and house cats also sleep when they are bored.
你是愛猫人士吗？你的手机里有多少张猫睡觉的照片？很多，对吧？它们睡觉的时候很可爱……很可爱。但是它们总是睡着的。好吧，不说总是，但很多时候都是。为什么会这样？
事实是猫平均每天睡15个小时。它们中的某一些把这个时间延长到了20个小时，特别是年龄更大的猫和小猫。这是可以理解的。但是什么让其他的猫也精疲力竭呢？
猫是天生的捕食者。它们的猎物动作又快又难以捉摸。悄悄靠近，再猛扑过去——反反复复地——这毫无疑问是累人的。野猫为了满足食物的需要而努力捕食，而消耗了这种体力则要补充大量的精力。
它们不仅仅是捕食者，它们是晨昏性捕食者，这意味着，在天微亮的黎明和黄昏时分，当它们的猎物——啮齿动物和鸟类——同样活跃时，它们的出行信号灯就会亮起来。一天里的其余时间，猫会睡觉，不过它们的睡眠有两种类型。
它们四分之三的睡眠是浅层的，几乎是醒着的。猫以一种预备的姿势打瞌睡，它们的嗅觉和听觉处于“开启”模式，耳朵偶尔会抽动一下。它们平静而沉着，随时准备做出反应：猛扑猎物，或者因为你在它们睡觉的时候鲁莽轻拍，而将你拍打抓挠得屁滚尿流。这种浅眠通常持续15到30分钟。
另外四分之一的睡眠时间里，猫真的睡得很沉。如果它们的爪子抖动看起来像在做梦，那是因为它们可能就是在做梦。
那我家里从不离开屋子的猫呢？为什么它总是睡觉？简言之，是因为遗传。作为一个物种，猫无论是在街上睡觉，还是在沙发上睡觉，都有同一个基本固定的生物钟。因此，家猫也会在无聊的时候睡觉。
（英语原文选自：www.britannica.com）
【Notes】
1. predator [