Z for snoring, and Japan

In Cecil’s article at http://www.straightdope.com/columns/read/3063/why-is-the-letter-z-associated-with-sleep , when describing how other cultures depict sleep or snoring in print or comics, he writes:

" The Japanese use characters that transliterate as “guu guu,” "

I’ve also heard that it’s a tradition in manga, anime, and Japanese video games, to depict a sleeping character by showing a bubble of snot expanding and contracting from one of his nostrils. (Hopefully not in comics you’ll be reading at the dinner table.)

Yes, that’s true: TV Tropes on “Snot Bubble”.