This way up

As part of a photography tour of London, we stood on the steps of the National Gallery in Trafalgar Square. There were some street acrobats promoting the Nissan Qashqai. I managed to take a photograph of the photographer who in turn was taking a photograph of the acrobat, just at the point when the acrobat was upside down. Fortunately, both were also wearing red t-shirts and dark trousers that matched the paving slabs. And it was a cloudy day, so there were no strong shadows. Lucky? Just a bit.