How it came about that snakes manufactured poison is a mystery. ^{主语从句套主语从句}

come about ^{to happen, especially in a way that is not planned （意外地事情）发生}

• Can you tell me how the accident came about?
• How did it come about that he knew where we were?
• That came about when we went to New York last year. ^{那件事发生在去年我们去纽约时。}

manufacture ^{(technical) if your body manufactures a particular useful substance, it produces it（身体）产生，制造，分泌}

• Vitamins cannot be manufactured by our bodies.
• Diabetics don't manufacture enough insulin.
• It may have been manufactured hours or days ago in your lungs. ^{它可能是几个小时前或几天前在你的肺里制造的。}

How it came about that ... is a mystery. ^{某个事情怎么发生的，是个谜}

• How it came about that Maya civilization vanished from the earth is a mystery. ^{玛雅文明是如何突然从地球上消失的，是一个谜}
• It has never been explained why Maya civilization vanished from the earth.
• It has never been explained why snakes manufactured poison. ^{课文写法替换}

Over the periods their saliva, a mild, digestive juice like our own, was converted into a poison that defies analysis even today.

defy ^{be so difficult as to make (sth.) impossible 无法…;使...不可能}

• Beauty sometimes defies description. 
• The problem defied solution.
• a political move that defies explanation
• It's a devastating and barbaric act that defies all comprehension. 

The beauty of the West Lake is more than words can describe. ^{be more than ... can / could ... 是...无法...}

be more than … can / could... ^{表达“是…无法…”}

• When my old friend Brian urged me to accept a cigarette, it was more than I could bear.
• Dancing proved to be more than the dish could bear, for during the party it capsized and sank in seven feet of water.
• The pain is more than I can bear. 
• The story is more than I can believe.
• The beauty of the West Lake is more than words can describe.
• The weather turned out to be very good, which was more than we could expect.

It was not forced upon them by the survival competition; they could have caught and lived on prey without using poison, just as the thousands of non-poisonous snakes still do.

force sth. on / upon sb. ^{把...强加给...}

• It's no good trying to force a diet on someone. 
• people who try to force their own views on you.

without using poison ^{如果不使用毒液（介词短语充当条件状语）}

• …; they could have caught and lived on prey if they had not used poison, … ^替换
• Without it we could not make a living.  ⇒ If we didn’t have it we could not make a living.
• Without it, nothing could ever be brought to a conclusion; everything would be in a state of chaos. ⇒ If we didn’t have it nothing could ever be brought to a conclusion; everything would be in state of chaos.
• There would be no living things without air. ⇒ There would be no living things if there were no air.
• In his position, I would have committed suicide. ⇒  If I had been in his position, I would have committed suicide.

just as ... still do ^{就像...仍然在做一样}

• … they could have caught and lived on prey without using poison, just as the thousands of non-poisonous snakes still catch and live on prey without using poison. ^课文补全

Poison to a snake is merely a luxury; it enables it to get its food with very little effort, no more effort than one bite.

luxury / necessity ^{奢侈品 / 必需品}

• Limousines and perfumes are luxuries while food, clothing, shelter and transportation are daily necessities.
• Mostly they climb as a necessity to make money. ^{他们大多把登山当作赚钱的必经之路。}
• Few could afford the luxury. ^{很少有人买得起这种奢侈品。}

no more than ... ^{仅仅，只不过}

• His answer was to lift the vessel out of the water by making it ride on a cushion of air, no more than one or two feet thick.
• When one seriously studies the social orders that have had the opportunity to develop autonomously, the figure becomes no more than an exact and matter-of-fact observation.
• Modern cloth diapers are surprisingly easy to use, almost no more work than putting on a disposable.

And why only snakes (manufacture poison)?

• My brother likes coffee, and I do, too. ^{(省略了 "like coffee")}
• She is taller than her sister. ^{(省略了 "is tall")}
• He eats more than I do. ^{(省略了 "eat")}
• Just waiting (now). ^{(省略了 "I am" 和 "now")}
• On the table (it is located). ^{(省略了 "It is" 和 "located")}
• You should tell him, but you don't have to. ^{(省略了 "tell him")}
• Ready for the trip? ^{(省略了主语 "Are you")}
• Given a choice, which would you pick? ^{(省略了主语和系动词 "If you are" 在状语从句中)}

Cats, for instance, would be greatly helped; no running fights with large, fierce rats or tussles with grown rabbits -- just a bite and no more effort needed.

Cats, for instance, would be greatly helped if they manufactured poison.  ^课文补全

running ^{adj.lasting a long time; continuous 持久的，长时间的}

• For years he had fought a running battle with the authorities over the land.
•  He also began a running feud with Dean Acheson.  ^{他也开始和艾奇逊院长发生接连不断的争执。}
• He said drought had led to severe crop failure for the second year running. ^{他说干旱已连续两年造成严重农作物歉收。}

tussles with ... ^{与...扭打，搏斗 a fight using a lot of energy, in which two people get hold of each other and struggle 扭打，搏斗}

• She had a brief tussle with her conscience before telling the whole story.
• They began to tussle with each other for the coin. ^{他们为争夺硬币扭打起来。}
• The referee booked him for a tussle with the goalie . ^{他和守门员拉扯，因而被裁判记名警告。}

In fact, it would be an assistance to all carnivores though it would be a two-edged weapon when they fought each other.

In fact, it would be an assistance to all carnivores ↔ In fact, it wouldbe an assistance to all carnivores if they manufactured poison. ^补全课文

two-edged weapon / sword ^双刃剑

• As is so often pointed out, knowledge is a two-edged weapon which can be used equally for good or evil.
• Mint forex reserve is a two-edged weapon, and it causes broad attention from the society. ^{外汇储备是把双刃剑，如此庞大的数字引起了社会的广泛关注。}
• Technology is a two-edged sword. ^{技术是一把双刃剑。}

when they fought each other ^{当它们互相搏斗时（when从句充当条件状语）}

• … though it would be a two-edged weapon if they fought each other.  ^课文替换
• How can I explain it to you when you won’t listen?
• When I reverse the car, it makes a funny noise. 

But, of the vertebrates, unpredictable Nature selected only snakes (and one lizard).

of ^{prep. used when comparing related things （用于比较时）在……中}

• I'm surprised that you of all people think that. 
• A flat tyre today of all days what bad luck!
• He's the best looking of the three brothers.

One wonders also why Nature, with some snakes, concocted poison of such extreme potency.

concoct ^{v.to produce sth. unusual by mixing things in a new way, esp. a drink or meal 调制}

• The soup was concocted from up to a dozen different kinds of fish.
• What was the most unusual fragrance or flavor you've had to concoct? ^{你配制的最奇怪的香水或者香味是什么？}
• But I'm going to need your help to concoct a story that will help me save face! ^{但你得帮我编造个故事，好给我留点脸面！}
• From within, you have chosen to concoct a multitude of excuses and a barrier of fear. ^{从你选择地炮制了许多借口和障碍恐惧。}

potency ^{the strength of sth., esp. a drug, on your mind or body 效力，强度}

• Improper storage may decrease the potency of the drug.
• The Numbers indicate the potency of the ingredient used. ^{数字是用来表示所用成份的效力的。}
• Perhaps his potency as a lover also had a physical explanation. ^{可能是他的性能力强大，也可能有其他体质解释。}