why is it that my Chinese co-workers spit so much?

phlegm ( P ) Pronunciation Key (flm)
n.
1. Thick, sticky, stringy mucus secreted by the mucous membrane of the respiratory tract, as during a cold or other respiratory infection.
2. One of the four humors of ancient and medieval physiology, thought to cause sluggishness, apathy, and evenness of temper.
3. Sluggishness of temperament.
4. Calm self-possession; equanimity.

I know that I'm not alone in my utter disdain and disgust at the practice some I work with choose to do in the bathroom sinks (and occasionally in the kitchen sink my whole floor shares) is it cultural?...perhaps...but it's no less fucking nasty...the Chinese were having a problem with it due to SARS in fact...perhaps I should spit so I can lay claim to my own sense of calm self-possession...or something...in other and completely unrelated news, I wonder if Bush will invoke the mass graves argument again tonight...mass graves != weapons of mass destruction