"shooting cigarette-size sticks of silver iodide into the clouds to induce precipitation."
Source(s):
http://www.digitaljournal.com/article/281441

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As others have said, sprinkling silver iodide into clouds. Basically, this lowers the temperature of the air, which means it can contain less moisture, meaning the moisture in the air condenses out of it into raindrops, which then fall.

As for why it makes you uncomfortable, it is because it feels like "messing with Mother Nature". (You're hardly the first to feel this way: google the lyrics to C.W. McCall's "Silver Iodide Blues" for a decades-old example.)

It's sort of the same reason that people react badly to nuclear power even though far fewer people have died from nuclear-power-related hazards than have died from, say, black lung disease caused by mining the coal for traditional power plants—or that people perceive air travel as hazardous though there are considerably fewer deaths per mile traveled in airplanes than in automobiles.

Gregory Benford wrote a really great column looking at this in the September 2000 issue of Fantasy & Science Fiction Magazine, which you can find via fulltext magazine indexes like EBSCO in your local library. Basically, the human capacity for judging risk is skewed in favor of things we can personally control, and against things that feel "unnatural".

Storytellers have long recognized this, and have spent decades going for cheap scares—writing story after story in which these "unnatural" things are demonized, and they have entered our mass subconscious to prejudice us against things like nuclear power, cloning, cloud seeding (a great example can be found in one of Bertrand R. Brinley's "Mad Scientist Club" story collections) and so on.
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The Chinese use silver iodide to seed clouds. The technique was devised in the USA in the 70's. It is safe, but only sometimes effective. Seeding clouds in this manner is and has been practiced in about 24 countries around the world.

The USA used similar seeding during the Vietnam War to muddy the enemy supply line. However, a treaty was signed in 1978 banning military use of weather modification.

As to why you are really uncomfortable, that is probably because you are ill informed, paranoid, and suspicious of whatever the Chinese may happen to be doing. Once you read up on the subject of cloud seeding and its history your comfort level will increase. Unless, of course, you start reading right wing conspiracy sites which have picked up on this as yet another nefarious Commie plot.
Source(s):
http://en.wikipedia.org/wiki/Cloud_seeding
http://www.springerlink.com/content/m7g2235u7v756668/
http://www.dri.edu/cloudseeding
http://science.howstuffworks.com/cloud-seeding1.htm
http://www.psychologytoday.com/articles/200501/conspiracy-theories-explaine...

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