actually if you try to hork (or whatever you call it), you sort of make a "hork" sound but it depends on the individual. "Hock" sounds American, i.e. the Brooklyn accent, so maybe the USA uses that...Canadians seem to add a bit of a French twist therefore..."hork." In any case it's a mixture of good old snot and spit. A few weeks back I was sick and it was such a relief to hork on a regular basis. Only time I dread it is when there's no place to spit it out and you're forced to swallow it...YUK!
I saw a shitty movie last week called "The Stoned Age" which was an even lower-budget movie than Dazed and Confused and the kid "horked" under the cusions of a couch. In other words, he vomited.