In the era of the internet, the only thing that spreads more rapidly than information, it seems, is awareness of a lack of information. And when facts are missing, the vacuum will soon fill up with theories, from the prosaic to the preposterous.
That's what has happened since September 1, the last time Xi Jinping was seen in public. As China's vice president and president-in-waiting, Mr Xi normally has a schedule studded with public events, but he has cancelled them all, including talks with a couple of visiting prime ministers and Hillary Clinton, the US secretary of state. China's leaders take protocol seriously; such cancellations are very rare.
So this has been an invitation to legions of Chinese bloggers, micro-bloggers and other internet denizens: Mr Xi is variously reported to have pulled a muscle swimming, to have hurt his back playing football, to be busy with a secret domestic crisis, to have suffered a heart attack, to have been hurt in a traffic accident staged by his enemies, and more. There has been no mention, so far, of alien abduction.
And yet Chinese officials refuse all comment, and some websites have blocked searches for his name. For all their power, China's leaders still have not discovered the reassuring value of candour.