Lesson 20-1 Snake poison
How it came about that snakes manufactured poison is a mystery. Over the periods their saliva, a mild, digestive juice like our own, was converted into a poison that defies analysis even today. 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. 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. And why only snakes? 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.
poison /ˈpɔɪzn/ 毒药，毒物，毒素;
saliva /səˈlaɪvə/ 唾液
digestive /daɪˈdʒestɪv/ 助消化的;和消化有关的
mild /maɪld/ 温和的;轻微的;和善的;
convert /kənˈvɜːrt/ 转换;转化;(使)转变;
defy /dɪˈfaɪ/ 不可能，无法(相信、解释、), 违抗;藐视;反抗
over the periods 经过很长时间
force upon 把……强加于……
prey /preɪ/ 猎物;受害者;受骗者
fierce /fɪrs/ 凶猛的
tussle /ˈtʌsl/ 扭打，争斗
