A hair of the dog?

This Korean language English textbook reads, "Oh, I'm miserable. I need a hair of the dog." At first, we were going to blog that this does not make any sense, and that we don't know what the author wanted to write. But, we goodsearched it, and learned that this is an English idiom that we never heard of.

The lesson, then, is to try to learn common English expressions first. You can use a phrase like this correctly, but it is so rare that many native speakers might not understand it. Also, there are many English-speaking countries around the world. Many phrases will only be understood in one country, and maybe even only a small region of that country.