求一个或几个英语关于动物谚语及其来由(小故事这样的)，谚语是中英文皆可的。

a black sheep 害群之马
be old dog at something. 就是对...有经验; 对...很内行的意思。
goose egg【俚】零分
like a drowned rat 浑身湿透（象落汤鸡）
like water off a duck's back 毫不在乎，毫无作用（如果你对侮辱、指责之类的不在乎可以用，如：Terry said he was too sensitive about criticism and he wanted to be like one of those people for whom it’s like water off a duck’s back）
to teach a fish how to swim 班门弄斧
a litte bird told me that 我听说的；有人私下告诉我的（一般不愿说出来源时所用）
a white elephant无用的累赘东西；沉重的负担
donkey's years 很长的时间
monkey uncle吃惊
rain dogs and cats倾盆大雨
a snake in the grass 潜伏的敌人，口蜜腹剑的人
monkey business胡闹，骗人的把戏；欺骗；恶作剧