A Coke Can or a Cardinal?

Perception is not reality

I am playing T'ai Chi outside at Harvard Business school very early one morning and I see a cardinal (bird, not prelate) flying around. Every now and then I see him as I turn, catch him out of the corner of my eye; but also every now and then I would think I see him only to find that my attention has been caught by a red Coke Can that someone has disca…