In the minds of Beijing's collectively stressed Olympics organisers, the list of things that could go wrong on the supposedly auspicious eighth day of the eighth month of the eighth year of the century - in other words, tomorrow - is long indeed. They suffered their latest panic attack on Monday. Police outside a barracks in the Muslim-populated Xinjiang region - which has been at the heart of the country's security fears for the past couple of months - were struck by a truck, then homemade grenades; 16 were killed and another 16 injured. The officials had another panic attack in the middle of last week. Video of a rehearsal of the opening ceremony - classified a 'top state secret' - became an instant hit on the internet after a reporter from a South Korean television station managed to walk into the National Stadium and shoot two minutes of footage. The organising committee went ballistic over the footage from the previously low-profile Seoul Broadcasting System, hammering it for lacking journalistic integrity and threatening punitive action. Possibly as a result, nearly all links to the footage vanished overnight, and the broadcaster apologised publicly - as fellow broadcaster CNN and actress Sharon Stone had done following other incidents during the tumultuous run-up to the Games. Given all the efforts to make the opening-ceremony spectacle a 'massive surprise to the world and satisfying to all Chinese people', in the words of its chief director, Zhang Yimou , the video leak was more than just annoying. It seemed a disturbing but genuine reminder that you never know what can spoil a party. It can be something big or small - hence Beijing's obsession with everything from controlling the weather to micromanaging people's behaviour. Officials have been trying their very best to anticipate and eliminate any possible challenge to the glorious coming-out party they envisage. A day with pollution so disastrous that it would force athletes to march into the 'Bird's Nest' with masks strapped to their faces remains a possibility strong enough to make Olympic environmental officers lose sleep. A last-gasp measure - taking another 10 per cent of the city's vehicles off the road and shutting down more factories - was proposed last week, but has not yet been implemented. And then there is the rain. State meteorologists say there is a 41 per cent chance of rain during the opening ceremony. If the worst were to happen, performers' costumes and props would be dampened, to say nothing of the festival mood. Some of the features most likely to wow the audience, such as dozens of airborne acrobats dressed as phoenixes - if the sneak preview courtesy of the South Koreans is to be believed - would have to be dropped. The next concern - given what happened in Kashgar on Monday - is security threats. Security has been an obsession of every host nation since the 1972 Munich Olympics, when 11 Israeli athletes were killed by Palestinian gunmen. So as tomorrow approaches - and some 80 heads of state arrive for the opening ceremony - precautions against terrorism are a must. The host nation has been talking up the threat from Muslim Uygurs in Xinjiang and has spoken of possible suicide attacks by Tibetans. The avowed goal of the Beijing Olympics has been subtly changed from the grandiose 'a green Olympics, a hi-tech Olympics and a people-centred Olympics' to the more down-to-earth 'a safe Olympics'. Terrorists are not the only worry; officials have been using the term 'security threat' liberally. No distinction is being made between violence and peaceful protests. Even behaviour in the stands or among parading athletes that poses no more of a risk than embarrassment to the host is considered a security threat. It's all about details, as they say. Lessons were learned from a concert in Shanghai five months ago when Icelandic singer Bjork yelled out 'Tibet, Tibet' after performing her song Declare Independence. Beijing officials now look out for potential problems to which they would normally have paid little heed. That would include preventing access to the stadium by spectators wearing politically incorrect clothing. The fear is that innocent-looking fans, or maverick athletes, may lift outergarments to reveal T-shirts with Tibet independence slogans. The officials' adrenaline levels would run even higher if they knew that activists were busy lobbying fans and athletes to wear orange - the colour of Tibetan Buddhist robes - tomorrow, or at the very least to flash the two-handed 'T for Tibet' sign. Organisers once pointed with pride to the Beijing Games' official logo - the arms-out dancing figure - and invoked the old Chinese saying: 'Is it not a joy to welcome friends from afar?' Now, with the opening ceremony just a day away, nervous rather than joyful would probably be a more accurate description.