If you're close to Nairobi City to see its tall buildings rising from the horizon, and if you happen to be standing at the side of the road waiting for a matatu to get you there, if it's your lucky day, you'll hear a makanga shout "Tao mbao! Tao mbao!" You'll get excited and you'll hurry to get into the matatu even as it begins to speed off. You'll have hardly settled down when the makanga will look at you expectantly, and you'll reach into your pocket. You'll shove aside the crinkly paper money and at the very bottom you'll find a single mbao, and you'll fish it out and hand it to the makanga, your thumb and index finger feeling its concentric circles between them.

You'll probably feel a tiny pang at having to part with such a particularly shiny new mbao, but as you hand over the familiar copper-nickel-aluminium-bronze coin, you'll have a slight smile on your face because really, it's such a steal.

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