(LI SHIGONG)

Anyone who has spent any time in the English-speaking world is likely to have heard of Sod's Law. Not a law of physics or mathematics, but one expressing a simple human truth: If a thing can go wrong it will go wrong (and usually at the most inconvenient moment). Sod's Law explains why the oven goes wrong when the boss is coming to dinner, why the train is running late when you are in a particular hurry, and why (in England at any rate) you always lose a filling or develop a toothache at a weekend or over a Bank Holiday when the dentists are closed.

So I shouldn't have been surprised that it was a Saturday afternoon in Beijing a few weeks ago that one of my teeth started to hurt. It actually hurt quite a lot. And the odd thing was that this was a tooth that had already had root canal treatment: With no nerve, it shouldn't have hurt at all. But although I tried to convince myself that it was my imagination, my tooth had other ideas. It was in pain. So, grumbling, reluctant and frankly slightly anxious I set about finding a dentist in Beijing.

I don't know anyone who actively enjoys going to the dentist. I'm sure dentists as a class are highly professional, charming, excellent spouses and parents and general assets to society. However, most of us would rather not see them unless we have to, or it's time for our six month check-up. And the idea of seeing a dentist in China was deeply perturbing. My Chinese vocabulary didn't stretch to "root canal treatment" and I wasn't sure that the grunts you emit instead of words when you're being drilled would be interpreted correctly. So poor Gao was confronted at short notice with a nervous tongue-tied foreigner who looked as though she had been hit in the face with a football.

I needn't have worried. The two hours I spent in Gao's dentist's chair were, if not exactly pleasurable, certainly one of my better dental experiences. Charm itself, he taught me the Chinese for root canal treatment, explained that the offending tooth had in fact two root canals (the cause of my problem), drilled it out, put in a dressing and told me to come back the following week. If I had any problems at all I should call him. My tooth was likely to be painful for a couple of days, but with ordinary painkillers it should be perfectly manageable.

I emerged from the dentist, my face still numb from the anaesthetic, delighted with Chinese dentistry and convinced that, for once, Sod's Law did not apply. My tooth had been sorted out quickly, cheaply and professionally and with far less hassle than I would have had in the UK. All I needed to do now was pop to the chemist and buy some Nurofen to get me through the next few hours.

Whereupon Sod, who had clearly been biding his time, decided to remind me that his Law is universally applicable. I headed straight for a well-known Hong Kong chain of chemists to stock up on painkillers, confident that they would stock the full range of Western over-the-counter medicine I'm used to seeing in Hong Kong. Wrong. Having walked along aisles of shampoo, vitamin tablets, Hello Kitty dolls, nappies and cosmetics, eventually I asked one of the shop assistants where the painkillers were. She looked at me as though I were mad. We don't sell those here, she told me, you have to go to a pharmacy for those. I explained that I didn't need prescription painkillers, just ordinary ones, but she was adamant. OK, I said, where's the nearest pharmacy? Unfortunately it appeared to be some way away.

My tooth was starting to throb and my temper to fray, but I eventually discovered the pharmacy and explained to the shop assistant (in my newly acquired dental vocabulary) that I'd just had root canal treatment and need some ibuprofen, as recommended by my dentist. She was having none of it. Ibuprofen wouldn't be strong enough. She offered me some other tablets she claimed were specially formulated for toothache. I stuck to my ground. Ordinary painkillers were all I wanted (and by this stage, given the increasing pain in my face, needed). She refused to sell me any, insisting that I should take her advice and have the tablets she suggested. Rather than embark on a "foreigner loses temper, face and dignity" situation I acquiesced and took them home, stopping at a friend's on the way to cadge some aspirin.

Five minutes on the Internet revealed that I'd been sold a strong antibiotic that produces serious side effects in some people and should never be taken with alcohol—an important fact the pharmacy assistant had completely failed to mention. Sod's Law indeed. The combination of excellent dentistry, non-availability of painkillers and random dispensing of strong drugs left me deeply confused. So next time (if there is a next time) I'll be back in Gao's chair having remembered to visit the airport chemist on my next trip back home.

The author is a Briton working in Beijing