split hair - to differentiate or argue on certain points or aspects that others consider to be minor details
鸡蛋里面挑骨头 - nitpick, to be anal (colloquial usage)
nitpick - to criticize on some inconsequential details
to be anal - usually applies to a person's action when that person is particularly sensitive on or overly concerned with certain things.
e.g. John is really anal on cleanliness when he dines in a restaurant. He would clean every piece of utensil before using them.