One of the men reached into his pocket to get out the money to pay. He pawed at a wedge of £10 notes. The cashier noticed a large gold ring on one of his fingers and saw what she thought was blood above his knuckles. Maybe he had been fighting? The cashier then glanced up. There was no break in their polite conversation. The customer had not noticed her looking, or perhaps the shopper did not even know his hand was bloody...