The little boy goes to school,the little dog following him every day

问题描述:

The little boy goes to school,the little dog following him every day
为什么不说:The little boy goes to school,the little dog follows him every day
为什么要用第一种说法?

逗号不能连接两句独立的句子,这里的following是现在分词表示伴随状态,也就是说这是一整句句子.
如果要像下面那句这么写就必须在当中用句号.