Black sheep (no!)

I'm reading "Fooled by Randomness: The Hidden Role of Chance in Life and in the Markets" (Nassim Nicholas Taleb) at the moment. It's not as good as I thought it would be from the reviews, but it's mildly interesting. He keeps going on about the "black swan" effect (that no matter how many white swans you see, that doesn't mean there are no black swans). Hence I was genuinely amazed when I saw a black swan on the River Cam today...