You have probably received one of those witty circular e-mails about the ridiculous things that happen only in movies. They do the rounds of the internet on a regular basis, morphing as recipients add their own candidates.

The best cliches from the one that dropped into my inbox last week were:

- The Eiffel tower can be seen from any window of any building in Paris.

- You will survive any battle in any war unless you show someone a picture of your sweetheart back home.

- It's always possible to find a parking space right outside the building you're visiting.

- A single match is usually enough to light up a room the size of a football stadium.

- When they are alone together, all foreigners prefer to speak English to each other.

Guns, padlocks and burning cigarettes

It should be added that plenty of things we don't raise an eyebrow about are also far-fetched. Last year, the US TV series Mythbusters dedicated an episode to 'mega movie myths', in which they debunked a series of action movie cliches. They proved, for example, that it's well-nigh impossible to break a padlock by shooting it with a handgun. One of my favourite cinematic myths is another of those we so often accept without applying the reality test: the fact that when someone slams a phone down, the person on the other end of the line hears a continuous tone. Go on - try it at home.

Another great movie trope - the explosive fire caused by a lit cigarette tossed nonchalantly onto a slick of petrol (The Birds, The Usual Suspects, Baz Luhrmann's Romeo + Juliet) - has recently been exposed as a highly improbable scenario in an experiment conducted by the US Bureau of Alcohol, Tobacco and Firearms.

What's really fascinating here is the way that the viral nature of the online world we now inhabit is gradually making us all more knowing. This is in many ways a good thing - it has made politicians more subject to public scrutiny than ever before, and given even the humblest couch potato the tools to recognise phenomena such as spin doctors and malfunctioning autocues.

But our default irony and cynicism is also making us more intolerant of those innocent absurdities that films have always thrived on. It has made children's movies less magical and more streetwise (then we had Cinderella, now we get Shrek). It has vaporised the star aura and replaced it with mere celebrity (then we had Garbo, now we get Paris Hilton). And it's also begun to make even the action film - which thrives on absurdity - self-conscious about its bulletproof heroes and impossible stunts.

To kill the hero off halfway through an action film when one of the bullets fired by his myriad assailants actually reaches its target would, of course, be unthinkable. So producers of action franchises - especially those that hope to reach out beyond the core male teen demographic - are forced to adopt other strategies. Casting, and scripting, against type is one such solution - offering up (as in Casino Royale) a rough-edged James Bond who looks uncomfortable in black tie, who seems happiest when he's using his fists and who, when asked whether he wants his dry martini shaken or stirred, replies 'Do I look like I give a damn''.

The other point of leverage in the new, post-modern action movie stems from the awareness that a film's style has a major effect on an audience's tolerance of unlikely events. Paul Greengrass' two Bourne films are a case in point. By using a handheld camera and the choppy editing techniques Greengrass had pioneered in docu-dramas like The Murder of Stephen Lawrence and Bloody Sunday, the director manages to gloss over the fact that some of the set-ups are as absurd as anything Sylvester Stallone has ever done.

Cutting to the chase

Think of the chase through the Moroccan casbah in The Bourne Ultimatum: fresh from being blown up by a roadside bomb, Matt Damon crosses town by jumping from (closed) window to (closed) window through a series of apartments. And he does so not to get to where he last saw the damsel in distress being hunted by the killer, but to where he has predicted they're going to be by the time he arrives. If it wasn't for the grainy, verite look of the footage, the adrenaline of the rapid-fire editing, the fact that the people in the apartments look genuinely shocked by Mr Damon's sudden appearance in a shower of glass, we'd write this off as just another far-fetched action sequence.

And we know at the back of our minds that it is. But the new handheld run-and-gun style makes a show of treating us like adults, so we return the favour by suspending our disbelief - for the time being.