The chief executive of a US company recently put a question to his board. Why was it, he asked, that so few of his 5,000 employees took the blindest bit of notice of the memos, videos and voicemail messages with which he continuously bombarded them? And why was it, he asked again, that anything remotely secret whipped around the entire company before you could say Jack Knife?

They pondered this uncomfortable truth for a while and decided on an experiment. They would start "rumours" by word of mouth, warning the person they tipped off to keep their lips zipped. Sure enough, the "secret" information was known by the entire company instantaneously.