I'm back in London visiting friends for the holidays, when it occurs to me that not only does it not feel like home any more, I have no idea how my native city works.

I realize this for the first time when I go to cross the road and nearly cause a traffic accident. Cars, it seems, are not content to simply drive around pedestrians as they are in Shanghai.

"I forgot that everyone uses the zebra crossings here," I think sheepishly, as drivers beep their horns angrily at me. "The Brits are such sticklers for rules."

I have also, it transpires, forgotten how the Metro works and keep embarrassing myself by trying to pay for things in yuan. When I ask for soy milk in the local corner shop, the owner looks at me as though I'm crazy. At our family Christmas dinner, it strikes me how much I miss rice.

By the third day I have decided that my birth country is an alien land, loosely disguised by the fact that I can read everything that's written and understand what people say, if not what they mean. "It's like being in America," I think in amazement. "Only less fat."