Scratch That

I subscribe to a neat little daily e-mail service called A.Word.A.Day, and today's word caught my attention, falling into that category of words, "I didn't know there was a word for that":

acnestis--The part of the body where one cannot reach to scratch.

What I really like is the etymology:

From Greek aknestis (spine), from Ancient Greek knestis (spine, cheese-grater).

"Cheese-grater"? The Ancient Greeks used the same word for "spine" and "cheese-grater"? That conjures up an odd mental image...