1.How it came about that snakes manufactured poison is a mystery.
蛇是怎样产生毒液的，这是一个谜。
How it comes怎么会……相当于why，在口语中用的比较多。
2.it enables it to get its food with very little effort, no more effort than one bite.
它使蛇不用费多大力气就能捕获到食物，轻咬一口即可。
no more than, not more than
no more than的意思是“只不过”，not more than的意思是“不多于”。试比较：
There are no more than ten tickles left.
剩下不到十张票。（有“票少”的含义）
The experiment was done by not more than 5 persons.
做这个试验的人不到五个。（没有“多”或“少”的含义，只是客观地说明数目）
This room is no bigger than that.
这个房间并不比那个大。（有“两个房间都不大”的含义）
This room is not bigger than that one.
这个房间不比那个大。（没有“两个房间都不大或都不小”的含义）
注：注意not…Any more than或no more…than在下面句子中的用法。如：
They cannot do the impossible any more than we can.
他们和我们同样不能做不可能的事情。
He is no more diligent than I am.
他和我同样不勤奋
no less than和not less than
no less than的意思是“不亚于”，not less than的意思是“不少于”。试比较：
There were no less than a thousand people at the meeting.
到会的有一千人之多。（有“到会人多”的含义）
There were not less than one thousand people at the meeting.
到会的至少有一千人。（没有“到会人多或人少”的含义）
This song is no less popular than that one.这首歌之受欢迎不亚于那首歌。（有“两首歌都受欢迎”的含义）
This song is not less popular than that one.这首歌受欢迎的程度不比那首差。（纯粹比较。不一定有“两首歌都受欢迎”的含义）
3.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.
譬如说，如果猫有毒液，那对猫会大有帮助，它就不必再和又大又凶的老鼠边跑边博斗了，也不必再和大兔子扭斗了，只要咬一口，就不必再费大力气。
for instance例如，相当于for example。
4.It is said that the nerve poison is the more primitive of the two, that the blood poison is, so to speak, a newer product from an improved formula.
It is said 据说，it形式主语，避免头重脚轻。
the more primitive of the two两者进行比较，两者中较……的一个。如果是三者或三者以上比较，则可以用最高级。
