The book
The Ambidextrous Universe by
Martin Gardner discusses this in great detail. I put it here, because it is one of the first things he mentions to get you to
think about
how mirrors work. He convinces you that it's impossible to tell an alien which side is left/right and then tortures you by hinting that there's a solution to the problem, and then says there isn't, and then says there is, and then explains a little, and then ...
He ended up saying something about the lines of what snol and kefabi and bigmouth_strikes said. Something about those lines because at that late in the book i was pretty sick and tired of
particle physics. I would have to read the book about 2 more times to actually follow what on earth he was
blathering about. In any case, if you want to start a really long conversation, mention this problem to some physicist at a party some time.
He also talks about what would happen if your parity was reversed. Bad Stuff. Drinking milk could kill you! Some stereo isomers (hopefully the word i mean) are actually parity-reversed versions of another substance. Often times rendering one distinguishing feature of a substance less apparent or potent in it's parity-reversed form. H.G. Wells also wrote a wonderful tale (called The Plattner Story) in his book 28 Science Fiction Stories. A chemist ends up in four-space and is thus able to turn himself around. (know how you can't rotate a 2 dimensional object front-to-back unless you move it in 3-space? Same idea). Martin Gardner liked this story, and so do I. The chemist ends up with his heart on his right side!