We Americans are famously overfed. Only in China did I realize that my eyeballs are fat and lazy too.

Before I came to China I read about China's 1.3 billion brains. In psychology classes, I read about experiments showing that when you give 100 American and Chinese people a picture to look at, the Americans spend most of their time staring at the middle, but Chinese eyes dart all over the picture.

But the experiments were all missing something: a reason. It's the mystery of 2.6 billion eyeballs.

That mystery had been running around in my mind, all the way to an elevator on a cold Beijing night. The old man next to me looked me and my bike up and down and said in Chinese: "Why don't you drive?"

I certainly don't bike to look cool. If I did, I wouldn't have bought a girl bike. I've never understood why men subject themselves to tiny seats and crossbars dangerously close to our manhood, when half the world's bikes are safer and comfier.

I realized in that elevator that biking around China had led me to a basic truth I would never have discovered on foot: the truth of 2.6 billion eyeballs.

Visitors to Asia often talk about reaching enlightenment on a Buddhist mountaintop, or in a terraced rice village. But my realization came on wheels, with terrifying heart palpitations.

It came when I dodged a taxi only to find myself face to face with a horse cart.

As I see it - from behind the curved handlebars of my girl bike - Chinese eyeballs dance around like ping-pong balls because they want to keep the brain behind them from spilling out.

There's so much happening in the streets of Beijing - motorized transport, horses going the wrong way down the street - that just staying alive is a nine-to-five for the eyeballs.

And besides the things that might flatten me, there are so many other things to look at, such as, is that baby pooping in a trashcan?

When I was young, my American eyes grew fat and lazy because the suburban streets were so empty of cars, bikes and other visual stimulation that they didn't have to work out.

But now, in China, they're as lean and nimble as hutong rickshaw drivers.

Since globalization seems to be flattening the world's cultures into a single being, are China's 2.6 billion eyeballs going to end up the same as America's 620 million eyeballs?

Fear not, I say. Bikes are slowly leaving China's streets, but its cars and unannounced U-turns are ensuring that these 2.6 billion eyeballs won't be getting lazy and fat anytime soon.

So to that old man in the elevator: I bike to discover truths like these - to experience life on street level, where most of those 2.6 billion eyeballs dart just like mine now do.