I have one hour left to get to the airport when I decide to stop at a cash machine. For all the great imponderables about living in a foreign country, it is the little things that intrigue and delight. Why don't fruit shops sell vegetables? Why do China's ground floors - like its babies - start at number one - leading me to travel down to the basement in every lift I entered during my first month in Shanghai? Why do all TV programs have subtitles? Why do PIN codes have six digits, not four?

One of these puzzles is why Chinese cash machines, unlike their European cousins, dispense their notes first and then the bankcard, and not the other way around.

"Another interesting quirk," I think, the first time I notice.

Cash first

Predictably, the morning I leave my bankcard in the machine I am running late for a flight. I take the cash and walk off, forgetting my card in the process. By the time I go back, it is too late. My card has gone.

I suddenly remember someone telling me that old people in China do not use cash machines because they do not trust them.

"Quite right," I think crossly. "Surely it would be more logical to give you the card back first. I am much more likely to forget the card than the money."

I call my infinitely kind Mandarin teacher Meimei for backup. On the way back to the bank, we practice key phrases for dealing with the situation.

"Repeat after me: 'the machine ate my card'," she says. "The machine ate my card."

"The machine ate my card," I say, feeling increasingly stupid.

We go into the bank. A cash desk teller looks up at us expectantly.

"The machine ate my card," I blurt out.

"You must have left it there," the teller says. "They don't just eat them for no reason."

"I'm sorry. Please can I have it back?" I ask.

"The machine only eats the card after more than two minutes. You must have left it there for at least two minutes."

"I'm really sorry," I say.

"You foreigners are always doing this," she says with a smile.

"I'm sorry, it's just that where I'm from the card comes out first, so I'm trained to expect it that way."

"We have loads of forgotten cards. Look how many cards we have. And the funny thing is, it's only foreigners who do this," she says.

I look at where a little graveyard of rainbow-colored bankcards sits piled up on the desk. The teller rifles through the pile.

After several minutes she identifies my card and starts to twiddle it between her forefinger and thumb.

"Please can I have my card," I say.

She looks at me, then looks down at the card, then looks back at me and says slowly. "How do we know it's yours?" At this point Meimei steps in with a flurry of incomprehensible Shanghai dialect, in her charming 'we're all from the same city' sort of way. I produce my bankbook with my card number on it and my passport with my name.

The teller hesitates. For a second I think she is about to hand over the card, but then she pulls back. "Your name and bank account number need to be on the same page. You'll have to go and get a certificate," she says triumphantly.

By now I have half an hour left to get to the airport. I rush to my bank to ask them to print out the document. While I'm there, I decide to take out some extra cash to be safe. "Please could I take out some money?" I ask the manager.

"I'm afraid you'll need your card to do that," he says.