yellow在形容人时有“胆怯、懦弱” 的意思，口语中常用a yellow dog 表示卑鄙的人。I really wonder why the two of them lead a cat-and-dog life?
The dog days or dog days of summer are the hot， sultry days of summer. They were historically the period following the heliacal rising of the star Sirius， which Greek and Roman astrology connected with heat， drought， sudden thunderstorms， lethargy， fever， mad dogs， and bad luck. They are now taken to be the hottest， most uncomfortable part of summer in the Northern Hemisphere.
这里的dog指某类人，常用语口语中，意识“家伙”，翻译时要依据上下文译成合适的词语。If you don't know how to skate， why don't you give the skates to me?
英文中，关于动物的歇后语、俗语、俚语有很多。但是这种用法经常会造成考生的误解。比如，在中文用语中通常具有贬义含义的“狗（dog）”，在英文中可绝不是在骂人。与中文的比喻类似，英文中引用动物的说法也都有其深层的含义。
