“jiǎo (腳)” can refer to the body part, which is a common concept. Since the Tang dynasty, the word “jiǎo” has been used as a common word, which has features of the ordinary shape, high frequency, and strong ability of word-formation. It can be illustrated by the fact that Grand Chinese Dictionary collects more than 600 entries that contain the morpheme “jiǎo”. Therefore, when not knowing the motivation of word-making, people find it easy for the word “jiǎo” to be borrowed for another character. The main reason for the shape error of “jiǎo” is found in the phonetic similarity. “zhǐ jiǎo couple (指腳夫妻)” has the shape error, so some people can only explain its meaning according to the text regardless of its formation reason. Others just undertake studies on the word “zhǐ (指)”, which can not provide the right answer, either. The form “zhǐ jiǎo (紙腳)” can refer to more than one word. Some of them are fake forms. These words marked by “zhǐ jiǎo” may not be received or collected completely, which is unhelpful for us to understand ancient books.